UC-NRLF 


ill 


B    3    Dbfi    b57 


illliiii 


Xo.  1795 


INSTRUCTIONS 

FOR  THE  CARE,  PRESERVATION,  REPAIR 
AND  ADJUSTMENT  OF 

INSTRUMENTS  FOR  THE 
FIRE-CONTROL  SYSTEMS 

FOR  COAST  AND  FIELD  ARTILLERY 


(TWELVE  PLATES) 


DECEMBER  18,  1906 
i^EVISED  NOVEMBER  J,  J909 
REVISED  OCTOBER  9,  I9I2     i^ 
REVISED  JANUARY  4,  J9I6 


WASHINGTON 

GOVERNMENT  PRINTING  OFFICE 

1917 


No.  1795 


INSTRUCTIONS 

FOR  THE  CARE,  PRESERVATION,  REPAIR 
AND  ADJUSTMENT  OF 

INSTRUMENTS  FOR  THE 
FIRE-CONTROL  SYSTEMS 

FOR  COAST  AND  FIELD  ARTILLERY 


(TWELVE  PLATES) 


DECEMBER  18,  1906 
REVISED  NOVEMBER  J,  1909 
REVISED  OCTOBER  9,  I9I2 
REVISED  JANUARY  4,  I9I6 


WASHINGTON 

GOVERNMENT  PRINTING  OFFICE 

1917 


War  Department, 
Office  of  the  Chief  of  Ordnance, 

Washington,  January  4,  1916. 
This  manual  is  published  for  the  information  and  government  of  the  Regular  Army 
and  Organized  Militia  of  the  United  States. 
By  order  of  the  Secretary  of  War: 

William  Crozier, 
Brigadier  General,  Chief  of  Ordnance, 
(3) 


365255 


INSTRUCTIONS    FOR     THE     CARE,    PRESERVATION,    REPAIR,    AND 

ADJUSTMENT  OF  INSTRUMENTS  FOR  THE  FIRE-CONTROL 

SYSTEMS  FOR  COAST  AND  FIELD  ARTILLERY. 


INSTRUMENTS. 

1.  The  instruments  used  in  the  fire-control  and  direction  system 
of  the  Coast  Artillery  include  the  following: 

Swasey  depression  position  finder,  types  A  and  All. 

Lewis  depression  position  finder,  types  A  and  B. 

Lewis  depression  position  finder,  model  of  1907. 

Eafferty  depression  position  finder,  type  B. 

Barr  and  Stroud  horizontal  base  range  finder. 

Azimuth  instrument,  models  of  1900,  1900  Mi,  and  1910. 

Telescopic  sight,  models  of  1896  M,  1897,  1898,  1898  M,  1899,  1902, 
and  for  14-inch  gun  turret. 

Two-inch  telescopic  sight,  models  of  1906  and  1909. 

Three-inch  telescopic  sight,  models  of  1904,  1910,  and  1912, 

Observation  telescope,  seacoast,  model  of  1908. 

Periscope  for  14-inch  gim  turret. 

Gunner's  quadrant,  model  of  1898. 

Elevation  quadrant,  model  of  1906. 

Elevation  quadrant  for  12-inch  mortar  carriages,  models  of  1891 
and  1908. 

Fire  commander's  plotting  board,  model  of  1906. 

Whistler-Hearn  plotting  board,  model  of  1904. 

Mortar  plottihg  board,  models  of  1906  and  1906  Mi. 

Three  hundred  and  sixty  degree  mortar  plotting  board,  model  of 
1911. 

Submarine  plotting  board,  model  of  1906. 

Pratt  range  board,  model  of  1905. 

Range  board,  model  of  1909. 

Deflection  board,  model  of  1905,  for  guns. 

Deflection  board,  model  of  1906,  for  12-inch  mortar. 

Wind-component  indicator. 

Set-forward  ruler. 

Prediction  scale. 

Predicter. 

Mine-prediction  ruler. 

Time-interval  recorder. 

(5) 


Drawing  boards,  battle  charts,  harbor  charts,  and  difference 
boards. 

Scale  arms  for  harbor  charts,  and  for  difference  boards. 

2.  The  instruments  used  in  the  fire-control  and  direction  system 
for  the  Field  Artillery  include  the  following: 

Weldon  range  finder. 

Field  Artillery  range  finder,  1  meter  base. 

Aiming  circle,  model  of  1916. 

Sextant  telemeter,  type  A,  model  of  1911. 

Battery  commander's  telesco'pe,  models  of  1904,  1905,  and  1915. 

Panoramic  sight,  models  of  1904  and  1915. 

Telescopic  sight,  models  of  1896,  1896  M,  and  1897. 

Rear  sight  of  various  designs  for  different  carriages. 

Front  sight  of  various  designs  for  different  carriages. 

Observation  telescope,  field,  model  of  1908. 

Range  quadrant  of  various  designs  for  different  carriages. 

Gunner's  quadrant,  models  of  1892,  1897,  and  1898. 

Plotting  board  for  mobile  artillery,  models  of  1905  and  1906. 

Field  Artniery  plotter,  model  of  1907. 

Battery  commander's  ruler. 

One-hundred-foot  steel  measuring  tape. 

3.  Other  instruments  include: 

Telescopic  musket  sight,  models  of  1908  and  1913. 
Sixty-foot  steel  measuring  tape  for  Weldon  range  finders. 

4.  In  preparing  instructions  for  the  care,  preservation,  repair, 
and  adjustment  of  the  above  instruments,  it  is  found  most  con- 
venient to  group  the  instruments  in  the  following  general  classes: 

(a)  Optical  instruments  proper,  including  the  telescopes  of  the 
various  depression  position  finders,  azimuth  instruments, 
telescopic  sights,  panoramic  sights,  observation  instruments, 
etc.,  and  Weldon  range  finders. 

(6)  Geared  instruments,  including  the  mechanical  features  of  aU 
instriunents,  designed  to  measure  accurately  angles  of  azi- 
muth, of  elevation,  or  of  depression,  as  the  azimuth  and  the 
elevation  and  depression  gears  of  the  various  depression 
position  finders  and  the  azimuth  gears  and  features  of  the 
various  plotting  boards. 

(c)  Scale  arms,  including  all  parts  of  instruments  provided  with 

scales  and  straight  fiducial  edges. 

(d)  Wooden  parts  of  instruments,  as  the  board  proper  of  the  plot- 

ting boards,  of  the  Pratt  range  boards,  of  the  time  range 
board,  of  the  deflection  boards,  of  the  drawing  board,  etc. 
ie)  Special  parts  of  instruments,  not  falling  in  any  of  the  above 
groups,  as  the  canvas  chart  of  the  Pratt  range  board,  the 
rubber  covering  of  the  mobile  artillery  plotting  board,  etc. 


5.  All  persons  using  any  of  the  instruments  referred  to  above 
should  be  thoroughly  familiar  with  the  various  descriptive  pamphlets 
issued  by  the  Ordnance  Department  relating  to  these  instruments. 
In  addition  thereto,  all  persons,  including  especially  armament  fore- 
men and  machinists,  called  upon  to  inspect,  repair,  or  adjust  any  of 
the  above  instruments  should  provide  themselves  with  the  working 
drawings  of  the  instruments  in  question  by  application  through  the 
proper  channels,  if  not  already  supplied  with  the  drawings  by  arma- 
ment officers.  Before  attempting  to  disassemble,  adjust,  or  repair 
instruments,  the  drawings  should  be  carefuUy  studied  and  a  thorough 
familiarity  thus  obtained  with  the  component  parts  of  any  mecha- 
nism and  with  the  function  of  each  part  in  the  train  of"  movements 
producing  any  given  result.  Complicated  groups  of  gear  wheels,  for 
instance,  should  never  be  separated  without  special  attention  to  the 
arrangement  of  the  group  and  to  the  sequence  of  the  varipus  disas- 
sembling operations  with  a  view  to  reversing  the  .above  operations  in 
proper  order  in  reassembling.  No  forcing  of  parts  together  should 
ever  be  tolerated.  When  such  forcing  seems  necessary,  the  indication 
is  that  the  parts  already  assembled  are  incorrectly  put  together. 

CARE  AND  PRESERVATION  OF  INSTRUMENTS. 

6.  The  care  and  preservation  of  instruments  is  properly  the  func- 
tion of  those  who  use  the  instruments.  Cleanliness,  freedom  from 
moisture,  dust,  dirt,  and  grit,  and  proper  oiling  are  of  first  impor- 
tance. By  proper  oiling  is  meant  the  supply  of  the  lubricating  oil 
specified  in  the  pamphlets  in  proper  amounts  and  at  proper  times. 
For  instance,  heavy  oil,  as  the  vaseline  used  in  the  azimuth-circle 
gear  of  the  panoramic  sight,  should  last  12  months  after  a  proper 
application.  Machine  oil  used  on  the  panoramic-sight  stem  needs 
frequent  renewal,  with  the  cleaning  of  the  parts  daily  or  oftener. 
Clock  oil  used  on  the  finer  gears  of  the  gun  center  of  the  Whistler- 
Hearn  board  will  last  ordinarily  from  four  to  six  months  without 
renewing,  depending  on  the  amount  of  use  received  by  the  board. 
In  this  latter  case,  frequent  or  excessive  oiling  actually  will  do  harm, 
as  the  excess  amount  will  flow  away  from  the  bearings  to  the  sur- 
rounding parts  and  serve  to  catch  dust  and  ultimately  to  clog  up  the 
parts  concerned. 

When  special  chests  or  cases  are  issued  with  instruments,  the 
instruments  should  habitually  be  placed  in  them  when  not  in  use; 
where  chests  or  cases  are  not  issued,  as,  for  instance,  in  the  case  of 
the  wind-component  indicator,  the  removal  of  dust,  excess  oil,  or  of 
the  moisture  which  collects  on  metal  surfaces  during  high  humidity, 
should  be  daily  attended  to  by  the  regular  caretaker. 


HUMIDITY. 

7.  One  of  the  most  important  points  to  be  observed  with  reference 
to  the  care  and  preservation  of  all  classes  of  instruments  is  the  pre- 
vention as  much  as  possible  of  the  deposit  of  moisture  from  the  atmos- 
phere. The  humidity  of  the  atmosphere  is  one  of  the  most  potent 
agents  in  producing  the  patina  or  film  on  the  lenses  and  prisms  of 
optical  instruments,  and  its  continuous  presence  on  the  surfaces  of 
the  optical  glass  will  render  them  unfit  for  use;  its  action  in  warping 
the  wooden  base  of  the  Whistler-Hearn  and  other  plotting  boards, 
drawing  boards,  deflection  boards,  and  Pratt  range  boards  is  pro- 
ductive of  trouble  and  frequently  necessitates  a  readjustment  of 
parts,  as,  for  instance,  by  means  of  the  slotted  screw  holes  in  the 
scales  of  the  gun  deflection  board;  its  action  on  steel  parts  is  to 
accelerate  rusting,  and  thus  not  only  to  mar  the  appearance  of  instru- 
ments, but  also,  in  the  case  of  gears,  pinions,  racks,  etc.,  to  destroy 
accuracy  and  prevent  easy  functioning.  It  is  not  always  possible 
absolutely  to  avoid  difficulty  from  this  source,  but  careful  covering 
and  oiling,  the  selection  where  possible  of  warm,  dry  places  for  the 
storage  of  optical  and  other  instruments  when  not  in  use,  and  the 
prompt  removal  of  deposited  moisture  wherever  discovered  will 
reduce  the  effect  of  humidity.  Especially  telescopic  sights  and  optical 
parts  of  instruments  should  be  stored  in  warm,  dry  places. 

The  condensation  of  atmospheric  moisture  on  the  lenses  or  prisms 
occurs  when  the  temperature  of  these  parts  is  lower  than  the  dew 
point.  The  evaporation  of  this  moisture  may  be  hastened  by  turn- 
ing on  the  lights  mounted  in  telescopes.  Heat  from  other  sources 
should  not  be  applied  directly,  as  it  may  result  in  unequal  expansion 
of  the  metal  parts  or  of  the  optical  parts  of  the  instrument  and 
cause  considerable  errors  of  observation. 

REPAIR  AND  ADJUSTMENT  OF  INSTRUMENTS. 

8.  Whenever  from  wear  due  to  long  service,  from  accident,  or  from 
any  other  cause,  an  instrument  is  rendered  unfit  for  service,  a  report 
of  the  case,  as  directed  in  the  following  extract  from  General  Orders, 
No.  47,  War  Department,  March  24,  1905,  should  be  received  by  the 
armament  officer. 

(1)  The  prisms  and  lenses  in  the  telescopes  of  position  finders, 
azimuth  instruments,  and  sights  are  not  arranged  for  ad- 
justment by  those  using  them.  The  taking  apart  of  tele- 
scopes for  any  purpose  and  the  making  of  any  adjustments 
other  than  those  provided  for  in  their  construction  and 
described  in  the  pamphlets  issued  by  the  Ordnance  Depart- 
ment, except  under  the  supervision  of  district  armament 
officers,  are  therefore  forbidden. 


(2)  When  telescopes  or  any  instruments  of  the  range-finding  and 
fire-control  system  for  mobile  and  coast  artillery  issued  by 
the  Ordnance  Department  require  repair,  a  report  describing 
the  character  and  extent  of  the  injuries  or  defects  will  be 
made  to  the  armament  officer  of  the  district.  In  case  the 
repairs  or  adjustment  required  by  telescopes  and  other  deli- 
cate instruments  of  precision  are  of  such  a  nature  that  they 
can  not  be  made  at  the  post,  as  above  specified,,  the  instru- 
ments will  be  shipped  by  express  to  such  arsenal  as  may  be 
designated  by  the  district  armament-officer. 

9.  The  armament  officer  of  the  district  in  which  the  repair  is  called 
for  will,  either  personally  or  through  his  proper  ordnance  foreman  or 
machinist,  make  an  inspection  of  the  instrument  reported  in  need  of 
repair  or  adjustment.  From  the  inspection  he  will  decide  whether 
the  telescope  or  other  delicate  instrument  of  precision  can  be  repaired 
at  the  post,  by  instrument  makers  or  watchmakers  in  the  vicinity,  or 
must  be  shippped  by  express  to  such  arsenal  as  he  may  designate.  In 
general,  in  shipping  instruments  away  from  posts  for  repair,  only 
such  parts  should  be  shipped  as  are  absolutely  necessary  to  a  proper 
repair.  Thus,  frequently  only  the  telescope  of  depression  position 
finders,  azimuth  instruments,  etc.,  need  be  shipped  when  they  only 
are  in  need  of  repair;  but,  on  the  other  hand,  if,  for  instance,  tide- 
scale  or  height-scale  parts  of  depression  position  finders  are  in  need 
of  repair  or  regraduation,  the  entire  instrument  must  be  shipped,  as 
aU  parts,  including  base  and  telescope,  will  then  be  required  for  the 
final  adjustment  after  regraduation. 

10.  The  regraduation  of  instruments  should  be  done  only  at  an 
arsenal  or  at  a  manufacturing  plant  equipped  with  accurate  graduat- 
ing machines.  All  other  repairs  of  an  extensive  nature  involving  a 
considerable  outlay  of  money,  including  the  obtaining  of  new  prisms 
and  lenses  or  of  new  castings  to  replace  broken  parts,  should  be  made 
at  an  arsenal. 

11.  Who  may  disassemble  and  repair  instruments. — Paragraphs 
marked  with  an  asterisk  (*)  are  added  for  the  use  of  instrument 
makers  in  the  adjustment  of  instruments  or  parts  of  instruments. 
It  is  not  intended  that  these  adjustments  shall  be  made  at  the  forts, 
but  only  at  those  places  such  as  arsenals  where  special  facilities  are 
provided. 

12.  The  parts  of  sights  and  fire  control  instruments  for  the  3-inch 
Field  Artillery  which  may  be  disassembled  by  the  battery,  are  speci- 
fied in  the  Handbook  for  3-inch  Field  Artillery  Materiel.  The  dis- 
assembling of  other  parts  will  be  performed  by  skilled  workmen  only. 

Prisms  of  sights  and  other  telescopes  will  not  be  removed  from 
their  holders  except  by  skilled  workmen.  As  a  general  rule  the  dis- 
assembling and  adjustment  of  sights  and  instruments  requiring  tools 


10 

other  than  those  issued  with  each  instrument  will  be  performed  only 
by  skilled  mechanics. 

13.  Screw  threads. — ^A  number  of  different  standards  of  screw- 
threads  below  ^-inch  diameter  have  been  used  on  sights  and  fire 
control  instruments.  They  are:  the  F.  A.,  the  V  thread,  the  U.  S., 
the  A.  S.  M.  E.,  and  the  British  Association.  The  F.  A.  standard 
thread  is  a  round  60°  thread.  Taps  and  dies  for  this  standard  are 
made  at  the  Frankford  Arsenal  only.  This  standard  is  used  on 
instrument  of  modelg  dated  prior  to  1905,  when  it  was  superseded 
for  new  design  by  the  V  thread  standard.  The  V  thread  is  a  sharp 
60°  thread.  Taps  and  dies  of  this  standard  are  procured  by  Frank- 
ford  Arselial  to  special  gauges.  The  V  thread  standard  was  super- 
seded for  new  design  in  September,  1909,  by  the  A.  S.  M.  E.  standard 
thread  which  was  recommended  for  adoption  in  1907  by  the  American 
Society  of  Mechanical  Engineers.  This  thread  is  now  the  standard 
thread  for  new  designs  for  all  screws  below  J-inch  diameter.  The 
U.  S.  standard  form  of  thread  is  on  screws  of  cap  screw  sizes  (varying 
in  diameter  by  -^  inch)  used  in  the  manufacture  of  the  azimuth 
instrument,  model  of  1900,  and  the  Swasey  depression  position 
finder.  An  independent  system  of  screws  with  U.  S.  standard  form 
of  threads  is  used  on  the  Lewis  depression  position  finder,  model  of 
1907.  Special  screws  with  U.  S.  standard  threads  are  found  in  other 
instances.  The  British  Association  screw  thread,  a  round  thread 
with  a  thread  angle  of  47^°,  is  used  on  Barr  and  Stroud  range  finders. 

No  holes  should  be  retapped  without  first  consulting  the  detailed 
drawing  to  ascertain  the  diameter,  pitch  and  type  of  screw  thread 
used.  In  case  the  proper  taps  are  not  on  hand,  they  should  be 
requisitioned  for.  Screws  for  the  various  instruments  are  kept  in 
stock  at  Frankford  Arsenal,  Benicia  Arsenal,  and  Manila  Ordnance 
Depot.  In  ordering  screws,  use  the  nomenclature  given  in  the 
pamphlet  descriptive  of  the  instruments  or  on  the  detailed  drawings. 
In  ordering  taps  state  the  standard,  the  diameter,  and  the  pitch. 

14.  In  describing  the  method  of  repair  and  adjustment  of  the 
instrmnents  already  listed  in  paragraphs  1  and  2  of  this  pamphlet, 
repairs  or  adjustments  of  instruments  will  be  taken  up  in  proper 
order,  according  as  they  may  faU  under  one  or  more  of  the  five 
groups  mentioned  in  paragraph  4. 

TOOLS    AND   FIXTURES   FOR   OPTICAL   REPAIR   WORK. 

(See  Plates  F,  G,  and  H  herewith  and  drawings  15-17-1  to  11,  inclusive.) 

15.  A  kit  of  tools  for  use  in  connection  with  optical  repair  work  is 
furnished  for  both  Coast  and  Field  Artillery.  The  list  of  tools  and 
fixtures  comprising  these  sets  will  be  found  on  Plate  H  herewith. 
Only  a  few  of  these  tools  wiU  require  description.     The  use  of  several 


11 

tools  and  fixtures  will  be  described  below  under  the  instructions  for 
repair  of  various  models  of  instruments.  Before  using  pedestal  No. 
85,  carefully  level  it  so  that  its  axis  is  vertical. 

16.  Collimating  telescope  for  Field  Artillery. — The  collimating  tele- 
scope (No.  90)  furnished  with  tools  for  Field  Artillery  work,  is  an 
ordinary  nonerecting  type.  It  is  adjusted  for  parallax  by  the  usual 
means  of  focusing  the  eyepiece  on  the  cross  wires  and  then  removing 
parallax  by  focusing  the  objective.  To  collimate  the  telescope  use 
the  horizontal  fixture  (No.  86)  mounted  in  pedestal  (No.  85),  holding 
the  telescope  against  the  guide  on  the  side  of  the  fixture  and  sight  on 
a  target  having  both  horizontal  and  vertical  lines.  Rotate  the  tele- 
scope on  its  axis  180°  and  if  the  cross  wires  do  not  coincide  with  the 
target,  correct  half  the  error  by  adjusting  the  reticule  by  the  reticule 
screws  and  half  the  error  by  shifting  the  telescope.  Repeat  until  the 
adjustment  is  found  to  be  correct.  Whenever  other  telescopes  can 
be  collimated  in  this  manner,  it  should  be  done. 

17.  Collimating  telescope  for  Seacoast  Artillery. — The  collimating 
telescope  (No.  98)  furnished  with  tools  for  Seacoast  Artillery  work  is 
the  ordinary  nonerecting  (astronomical)  type  with  Ramsden  eye- 
piece. The  aperture  of  its  objective  is  1  inch.  The  power  is  8  and 
the  field  of  view  is  3°.  The  draw  tube,  operated  by  a  focusing  ring, 
provides  for  the  removal  of  parallax  between  the  image  and  the 
reticule.  The  eyepiece  is  adjustable  for  focusing  on  the  reticule. 
The  cross-wire  ring  is  held  in  position  by  four  screws  and  washers. 
The  collimation  adjustment  for  this  telescope  is  similar  to  that 
described  above  in  paragraph  16. 

To  disassemble  the  draw  tube,  remove  the  screw  holding  the  focus- 
ing ring  cap  to  the  focusing  ring  (see  drawing  15-17-10),  unscrew  the 
cap  and  pull  out  the  draw  tube.  The  eyepiece  is  retained  in  the  draw 
tube  by  a  retaining  screw.  The  objective  cell  is  also  locked  in  the 
tube  by  a  retaining  screw. 

With  the  telescope  is  a  bracket  for  use  in  collimating  telescopic 
sight,  model  of  1899,  and  rings  which  fit  the  outside  bearing,  surfaces 
of  the  tube  and  which  adapt  the  collimating  telescope  for  use  in  the 
telescope  seats  of  the  telescopic  sight,  model  of  1902,  the  3-inch 
telescopic  sight,  model  of  1904,  and  the  2-inch  telescopic  sight,  modal 
of  1906. 

CLINOMETER,   MODEL   OF    1909. 

18.  Use. — This  instrument  is  provided  for  the  checking  of  elevation 
scales.  To  use  it,  set  up  the  clinometer  on  a  clinometer  rest.  Level 
the  cross  level  using  the  adjusting  screw.  Do  not  clamp  the  adjusting 
screws  too  tightly.  Level  the  elevation  level  by  means  of  the  eleva- 
tion mechanism  of  the  gun  or  mortar  on  which  the  clinometer  is  used. 
Reverse  the  clinometer  and  relevel  the  cross  level,  if  necessary.     In 


12 

case  the  elevation  level  vial  bubble  is  not  central  as  before,  correct 
half  the  error  by  adjusting  the  vernier  by  means  of  the  vernier  adjust- 
ing screw  and  half  the  error  by  means  of  the  elevating  mechanism  of 
the  gun  or  mortar.  Repeat  the  operation  to  verify  the  adjustment. 
Care  should  be  taken  to  loosen  the  vernier  clamping  screw  before 
adjusting  the  vernier  and  to  tighten  it  after  adjusting  it. 

To  set  the  clinometer  to  a  given  elevation,  imclamp  the  slow-motion 
clamp,  grasp  the  carriage  on  a  surface  as  near  as  possible  to  the  T 
guide  surface  of  the  support  and  slide  the  carriage  to  the  approximate 
position  desired.  Then  clamp  the  slow-motion  clamp  and  make  final 
adjustment  by  means  of  the  slow-motion  screw. 

The  least  reading  of  the  clinometer  is  1  minute.  A  movement  of 
the  bubble  of  the  elevation  level  of  0.1  inch  corresponds  to  30  seconds 
of  arc. 

19.  Adjustment. — The  elevation  level  is  adjusted  by  means  of  the 
horizontal  adjusting  screws  so  that  if  the  elevation  level  is  set  level, 
the  clinometer  may  be  rotated  several  degrees  on  the  clinometer  rest 
without  being  moved  out  of  its  level  position.  The  elevation  level  is 
adjusted  by  means  of  the  vertical  adjusting  screws  to  allow  for  setting 
the  0  mark  of  the  vernier  correctly. 

The  cross-level  bubble  should  be  central  when  the  support  is  ver- 
tical, and  it  should  remain  central  while  the  gim  or  mortar  is  elevated 
a  few  degrees,  or  the  carriage  is  sUd  over  the  support  a  few  degrees. 
A  test  of  the  correctness  of  the  adjustment  of  the  cross  level  should 
preferably  be  made  when  the  elevation  level  is  approximately  level. 
The  vertical  adjusting  screws  are  adjusted  so  that  the  cross  level 
indicates  level  when  an  accurate  machinist's  level  laid  across  the  top 
surface  of  the  support  at  right  angles  to  it  indicates  level.  The 
horizontal  adjusting  screws  are  adjusted  so  that  the  bubble  of  the 
cross  level  remains  central  as  the  gun  or  mortar  is  elevated. 

OPTICAL.  INSTRUMENTS  (Group  a). 
GENERAL   CONSTRUCTION. 

20.  The  construction  of  optical  systems  of  service  instruments 
vary  from  that  of  the  simple  GalUlean  and  astronomical  telescopes 
to  the  intricate  systems  of  the  periscope  and  the  horizontal  base 
range  finders.  The  larger  number  of  telescope  systems,  however, 
consist  of  an  objective,  an  erecting  system,  and  an  eyepiece.  In 
some  telescopes,  as  the  battery  commander's  telescope,  for  example, 
additional  prisms  are  used  for  the  deflection  of  the  entrance  pencil 
90°,  in  order  that  the  axis  of  the  telescope  may  be  made  vertical. 
The  periscope  systems  include  a  combination  of  prisms  so  mounted 
that  the  image  remains  erect  and  the  eyepiece  in  a  fixed  position 
during  the  rotation  of  the  periscope  head  through  a  complete  circle. 


13 

In  horizontal  base  range  finders  special  prism  systems  for  accomplish- 
ing a  sharp  division  of  the  field  as  well  as  the  erection  of  the  image 
are  employed. 

21.  Objectives. — The  objectives  of  service  telescopes  consist  of 
combinations  of  two  or  three  lenses  which  are,  with  few  exceptions, 
combined  to  prevent  spherical  aberration  and  are,  with  the  exception 
of  the  larger  objectives,  cemented.  When  two  lenses  or  a  doublet 
is  used  it  consists  of  a  crown-glass  convergent  lens  and  a  flint-glass 
divergent  lens.  The  crown  or  the  flint  may  be  in  front;  depending 
upon  the  optical  characteristics  of  the  glass.  When  three  lenses  or 
a  triplet  is  used  it  consists  either  of  two  collective  crown-glass 
lenses  and  a  flint-glass  dispersive  lens,  the  fhnt  being  the  central 
lens,  or  of  two  flints  and  a  crown,  the  crown  being  on  the  inside. 
In  some  telescopes,  as  that  for  the  Swasey  depression  position  finder, 
the  objective  is  centered  in  the  tube  by  means  of  coUimating  screws, 
but  ordinarily  the  optical  axis  of  an  objective  is  not  adjustable 
in  respect  to  the  axis  of  the  tube.  In  the  latter  class  of  instruments 
the  telescope  is  collimated  by  adjusting  the  cross  wires  to  bring  their 
intersection  into  the  optical  axis  of  the  objective. 

22.  Erecting  systems  .^-Erecting  systems  are  of  various  types  con- 
sisting of  lenses  or  of  prisms.  The  lens-erecting  system  consists 
of  two  or  more  lenses  inserted  in  the  telescope  system  in  the  rear 
of  the  focal  plane  of  the  objective,  usually  in  the  eyepiece,  and  so 
constructed  as  to  form  a  positive  image  of  the  image  formed  by 
the  objective.  By  it  the  inverted  image  of  the  objective  is  rein- 
verted.  In  the  simpler  form  the  system,  together  with  the, eye- 
piece, is  known  as  the  Fraunhofer  eyepiece  or  terrestrial  eyepiece. 
This  system  is  used  in  the  telescopic  sight,  model  of  1899.  In  a 
modified  form  of  this  system,  such  as  used  in  the  telescopic  sight 
for  14-inch  turret  mount,  the  simple  lenses  are  replaced  by  cemented 
combinations  in  order  to  secure  improved  optical  qualities. 

23.  The  earher  prism-erecting  system  used  in  service  telescopes 
is  the  Brashear  Hastings  erecting  prism  shown  on  Plate  A.  This 
prism  consists  of  two  30°  triangular  prisms  cemented  to  the  base 
of  a  prism  of  pentagonal  section  with  90°  roof  angle.  The  path  of 
the  axial  ray  is  shown  on  Plate  A.  The  efficacy  of  this  group  of 
prisms  depends  not  only  on  the  correct  angular  relation  of  the  various 
surfaces  but  also  upon  the  proper  assembMng  of  the  components. 
In  it  the  roof  angle  is  required  to  be  ground  within  an  extremely 
smaU  angular  error. 

The  Porro  system  of  erecting  prisms  is  shown  in  Plate  C.  The 
system  consists  of  two  right-angled  triangular  prisms  mounted  with 
their  axes  at  right  angles  to  each  other  and  with  the  half  of  the 
hypothenuse  faces  of  each  overlapping.  The  path  of  the  rays  being 
bent  back  upon  itself  permits  a  shortening  of  the  telescope.     For 


14 

these  reasons  the  Porro  system  has  superseded  the  Brashear  Hastings 
system  in  sei-vice  telescope  construction. 

A  Porro  erecting  system,  modified  for  a  telescope  with  a  vertical 
axis,  is  shown  in  Plate  E. 

24.  The  periscope  prism  system  consists  of  three  prisms.  See 
Plate  E.  The  right-angled  deflecting  prism  is  connected  with  the 
erecting  prism  so  that  during  the  revolution  of  the  former  through 
a  complete  circle  the  latter  rotates  with  half  the  angular  velocity 
of  the  former.  The  optical  effect  of  the  system  is  the  inversion  of 
the  image  and  the  nonrotation  of  the  image  during  the  rotation 
of  the  system.  The  image  which,  however,  is  reversed  right  for 
left  is  corrected  by  means  of  an  additional  prism. 

25.  Eyepieces. — ^Among  the  numerous  types  of  eyepieces  foimd  in 
service  telescopes  are: 

The  negative,  consisting  of  a  divergent  lens  as  used  in  the  tele- 
scope of  the  sextant  telemeter. 

The  Ramsden,  consisting  of  two  simple  convergent  lenses  of 
equal  focal  length  and  separated  by  a  distance  equal  to  two -thirds  of 
the  focal  length  of  a  lens. 

The  Kellner,  a  modified  form  of  the  Ramsden  eyepiece,  in  which 
a  single  eye  lens  is  replaced  by  a  cemented  doublet  with  plane  face; 
for  example  see  Plate  A.     This  class  is  largely  used. 

The  Steinheil,  consisting  of  a  cemented  triplet  with  the  crown  col- 
lective element  inside.  This,  for  example,  is  found  in  the  musket 
sight. 

A  special  development  of  the  Ramsden,  the  orthoscopic  in  which 
the  field  lens  consists  of  a  triplet  and  the  eye  lens  of  a  plano-convex 
lens  with  small  separation.  For  example,  that  used  with  the  obser- 
vation telescope,  seacoast,  model  of  1908. 

The  terrestrial  or  Fraxmhofer  eyepiece,  in  which  an  erecting  system 
is  combined  with  the  eyepiece  proper. 

With  the  exception  of  the  telescope  in  which  the  first-mentioned 
divergent  class  of  eyepieces  is  used  all  have  fields  in  which  a  reticule 
may  be  placed. 

26.  Adjustment. — Each  lens  of  an  optical  system  is  designed  to 
reduce  the  aberrations  of  the  system  to  a  minimum.  This  design  is 
based  upon  calculations  in  which  is  considered,  among  other  things, 
the  optical  qualities  of  the  glass  used,  the  direction  in  which  fight 
traverses  the  system,  the  separation  of  lenses  and  the  curvature  of 
each  surface.  Due  to  the  nimierous  conditions  involved,  the  curva- 
ture of  each  surface  is  special.  After  test  of  the  elements  of  a  system 
they  are  assembled  and  the  system  is  adjusted  for  the  best  results. 
Thus  for  the  proper  performance  of  an  optical  system  there  is  but  one 
way  in  which  the  components  of  a  compound  lens  or  system  may  be 
assembled,  and  but  one  distance  at  which  the  elements  of  a  system 


15 

may  be  spaced.  Thus  the  importance  of  the  instruc,tions  given  below 
to  mark  each  element  to  indicate  the  direction  in  which  Ught  traverses 
the  system  and  the  relation  of  components  to  each  other.  Failure 
to  observe  these  instructions  will  cause  imperfect  definition  by  an 
increase  in  the  spherical  aberrations  and  in  many  cases  increased 
errors  in  curvature  of  the  field  and  distortion.  In  some  cases  the 
impairment  in  definition  may  not  be  noted  except  by  an  experienced 
observer,  but  it  will  be  sufficient  to  cause  eye  strains. 

OPTICAL   DEFECTS. 

27.  Chemical  disintegration  of  optical  glass  is  caused  by  the  action 
of  moisture,  dust,  and  acid.  Water  is  taken  into  composition  in  the 
surface  layers  of  the  glass  and  the  alkahne  contents  of  the  glass  set 
free.  The  resistance  of  glass  to  decomposition  depends  upon  its 
chemical  composition.  Dust  causes  what  is  known  as  lead  spotting — 
the  formation  of  brown  spots  of  irregular  outlines  or,  in  the  more 
advanced  stages,  the  covering  of  the  whole  surface  with  a  brown  film. 
Flint  glasses  used  in  the  divergent  elements  of  lenses  are  especially 
sensitive  to  attacks  of  this  nature.  The  decomposition  is  due  to  the 
action  of  the  weak  organic  acids  present  in  dust.  Among  acids  which 
decompose  optical  glass  is  acetic  acid,  which  is  present  in  the  per- 
spiration of  the  body.  Thus  the  caution  against  the  leaving  of  finger- 
marks on  optical  surfaces. 

The  decomposition  of  optical  glass  by  weathering  is  due  to  the 
action  of  both  water  and  acids  present  in  dust  or  elsewhere.  The 
form  of  decomposition  ordinarily  observed  is  lead  spotting.  The  rate 
of  decomposition  increases  with  the  temperature.  It  is  especially 
rapid  in  the  warm  moist  cHmate  of  the  Tropics.  Thus  greater  pre- 
cautions are  required  in  warm  climates  than  in  the  cooler  regions. 

Decomposition  first  appears  ordinarily  on  the  flint  of  objectives 
and  the  exposed  plane  surface  of  the  flint  of  the  eye  lens.  The  crowns 
of  some  objectives  are  also  subject  to  attack.  The  glass  used  in 
prisms  is  comparatively  not  subject  to  decomposition 

To  examine  an  optical  surface  for  evidences  of  decomposition 
hold  the  piece  so  that  the  Ught  of  bright  daylight  is  reflected  by  it 
nto  the  eye.  Focus  the  eye  on  the  glass  surface.  It  is  seldom  that 
any  surface  defects  will  be  apparent  in  light  transmitted  by  the 
piece. 

The  surface  decomposition  detracts  from  the  efficiency  of  any 
optical  element  by  reducing  the  amount  of  Ught  transmitted  by  the 
system.  To  remove  the  affected  surface  repoHshing  is  necessary. 
This  work  should  be  done  only  at  an  arsenal  or  a  properly  equipped 
optical  shop. 

28.  The  balsam  used  in  cementing  compound  lenses  or  prisms 
sometimes  dries  and  cracks,  the  effect  being  observed  in  a  delicately 


16 

formed  tracery  somewhat  resembling  frost  markings  in  shape  in  the 
case  of  prisms,  and  small  bright  disks  in  the  case  of  achromatic 
lenses.  Whenever  this  becomes  sufficiently  pronounced  to  observe 
the  image,  the  telescope  of  the  instrument  affected  should  be  sent  to  an 
arsenal  for  overhauling.  In  no  case  should  the  recementing  of 
prisms  and  lenses  be  attempted  at  posts. 

CLEANING  AND   KEADJUSTING. 

■  29.  Cleaning. — For  cleaning  optical  surfaces  use  the  cloth  and  the 
special  lens  paper  furnished  for  that  purpose.  An  old  soft  linen 
handkerchief  is  also  good.  Under  no  circumstances  use  dirty  cloths, 
dirty  chamois  skins,  cotton  waste,  or  similar  materials.  A  camel 
hair  brush  is  excellent  for  removing  dust  or  lint.  In  case  a  solvent  is 
required  in  cleaning,  alcohol  should  be  used.  It  is  permissible  to 
breathe  upon  the  surface,  but  not  to  spit  upon  it.  Saliva  causes 
deterioration  of  lenses.  Water,  as  explained  above,  is  also  harmful. 
It  is  preferable  that  it  be  not  used  except  in  very  small  quantities,  as 
from  the  condensation  of  the  breath. 

In  cleaning  take  care  to  remove  with  a  brush  all  particles  which 
might  scratch  the  surface.  Then  moisten  the  surface  with  alcohol 
or  the  breath  and  wipe  it  carefully.  Then  dry  it  with  a  clean  cloth  or 
paper  and  wipe  off  any  remaining  lint  with  a  soft  brush.  While 
cleaning  take  care  that  the  fingers  do  not  come  in  contact  with  a 
polished  surface.     Also  do  not  allow  any  oil  to  reach  the  glass. 

30.  Cleaning  lenses. — In  disassembling  compound  objectives  for 
cleaning,  unscrew  the  cell  retaining  ring  and  carefully  push  the 
objective  from  its  ceU,  noting  which  surface  is  the  front  surface  and 
without  disturbing  the  relative  position  of  the  component  lenses. 
Mark  an  arrow  (A )  across  the, periphery  of  the  lens,  the  point  of  the 
arrow  toward  the  front  surface.  While  cleaning  do  not  wipe  off  the 
marks.  With  the  aid  of  the  arrow  in  reassembling,  preserve  the 
original  relation  of  all  the  optical  surfaces.  The  elements  of  a  com- 
poimd  lens  should  be  separated  by  a  ring  of  thin,  preferably  black, 
paper.  In  case  a  ring  is  not  available  stick  three  small  narrow  pieces 
of  paper  near  the  edge  of  each  surface  to  prevent  the  glass  surfaces 
from  coming  into  contact  with  each  other.  Reassemble  the  compound 
lens  in  its  cell  with  the  same  surface  to  the  front  as  originally  found. 

In  removing  lenses  from  their  cells  and  in  inserting  them  do  not 
bring  too  much  pressure  to  bear  upon  them.  The  flint  element  is 
especially  liable  to  be  broken.  The  cells  are  made  of  slightly  larger 
diameter  than  the  lens  and  if  not  wedged  by  tilting  the  lens  should 
freely  seat  itself.     Chipping  the  edges  should  be  avoided. 

A  compound  lens  should  not  be  removed  from  its  ceU  unless,  after 
cleaning  the  exposed  surfaces,  it  is  found  that  the  interior  surfaces 


17 

also  require  cleaning.  This  will  be  seldom.  Under  no  circumstances 
attempt  to  remove  a  lens  that  is  burnished  or  crimped  in  its  cell. 
Such  lenses  are  cemented. 

The  lenses  of  eyepieces  are  ordinarily  burnished  in  cells  which  are 
screwed  into  an  eyepiece  tube.  For  cleaning,  unscrew  the  cells  but 
do  not  remove  the  lens  from  its  cell.  If  the  cells  are  of  the  same 
diameter  note  before  disassembling  the  order  in  which  the  lenses  are 
assembled  and  reassemble  in  the  same  order. 

31.  Cleaning  Br asJiear- Hastings  prisms. — ^The  Brashear-Hastings 
erecting  prism  is  supported  in  a  metal  holder  by  a  crossbar  and  two 
screws  (see  Plate  B)  for  adjustment  of  the  line  of  collimation.  The 
prism  may  be  rocked  on  the  cross  bar  by  means  of  the  screws.  In 
adjusting  care  should  be  taken  to  bring  a  slight  pressure  to  bear  on 
each  screw  but  not  to  strain  the  prism.  On  gun  sights  after  adjust- 
ment the  space  between  the  prism  and  its  holder  is  fiUed  in  with 
plaster  of  paris.  In  tiftie  the  plaster  will  crumble  and  require  replace- 
ment. Examine  the  plaster  of  paris  once  a  year  and  without  straining 
them  test  the  prism  adjusting  screws  to  see  that  they  have  not 
loosened.  Do  not  remove  the  prism  from  its  holder  for  cleaning.  All 
surfaces  may  readily  be  cleaned  without  removal.  Take  especial 
care  not  to  chip  the  edge  of  the  roof  of  the  prism.  After  cleaning 
look  through  the  prism  to  detect  any  trace  of  the  deterioration  of  the 
balsam. 

When  reassembling  the  prism  holder  in  its  seat  take  especial  care 
to  seat  properly  the  dowel  pins  and  to  screw  up  tightly  the  prism 
holder  screws. 

32.  Cleaning  Porro  prisms. — Porro  prisms  are  ordinarily  held  in 
milled  seats  by  springs  as  shown  in  Plate  C.  Generally  it  wiU  be 
sufficient  to  clean  only  the  exposed  surfaces,  in  which  case  do  not  re- 
move the  prisms  from  their  seats.  In  case  it  is  necessary  to  remove 
the  prisms,  carefully  mark  each  prism  so  that  it  may  be  assembled  in 
the  same  seat  and  without  turning  it  end  for  end.  Sometimes  notches 
are  cut  in  prisms  as  an  aid  in  assembling,  but  this  is  not  always  the 
case.  To  avoid  interchanging  it  is  advisable  to  disassemble  but  one 
prism  at  a  time.  These  precautions  are  necessary,  as  it  is  imprac- 
ticable to  grind  the  angles  of  a  prism  without  appreciable  error,  and 
interchange  or  reversal  when  assembling  will  change  the  position  of 
the  opticle  axis  of  the  instrument. 

33.  Tests. — The  correctness  of  assembling  and  the  accuracy  of  ad- 
justment of  an  optical  system  may  be  tested  by  noting  its  definition 
and  its  freedom  from  errors.  Ordinarily  a  test  for  definitioil,  or  the 
cleanliBSS  and  distinctness  with  which  objects  appear,  is  sufficient. 
Make  the  test  on  clearly  defined,  distinct,  distant  objects,  preferably 
on  objects  which  stand  out  in  sharp  relief  against  a  light  background, 

9950—17 2 


18 

such  as  lighthouses,  stacks,  poles,  etc.  Observe  the  sharpness  with 
which  the  details  of  the  objects  are  brought  out  in  all  parts  of  the 
field  of  view.  The  quality  of  a  telescope  may  best  be  determined  by 
comparison  with  other  telescopes,  preferably  with  those  of  the  same 
power. 

No  telescope  image  is  entirely  free  from  errors,  but  in  all  systems 
the  residual  errors  should  not  be  sufficient  to  impair  good  definition 
or  to  interfere  with  the  efficient  use  of  the  telescope. 

In  all  telescope  images  it  will  be  observed  that  a  color  fringe  borders 
the  outlines  of  well-defined  objects.  If  the  fringes  are  of  yellow  or 
purple  color  they  are  due  to  a  residual  chromatic  aberration  which 
it  is  not  practicable  to  remove  in  manufacture.  If,  however,  a  fringe 
of  a  distinct  red  or  blue  color  is  visible  in  the  center  of  the  field  some 
part  of  the  optical  system  is  out  of  adjustment  or  the  elements  are 
not  properly  corrected.  Faults  of  this  nature  will  most  likely  be 
found  in  terrestrial  eyepieces. 

Practically  all  objectives  contain  small  errors  known  as  spherical 
aberration,  but  in  no  objective  should  the  amount  be  large.  It 
may  be  increased  by  the  reversal  of  lenses,  especially  of  objectives. 
An  appreciable  increase  will  impair  the  definition  of  the  telescope. 
To  measure  the  spherical  aberration,  cover  aU  of  the  objective  except 
a  small  circle  about  i  inch  diameter  at  its  center.  Remove  parallax 
from  the  telescope  and  note  the  position  of  the  draw  tube.  Then 
cover  all  the  objective  except  a  narrow  ring  near  its  periphery  and 
again  remove  parallax.  Measure  the  difference  in  the  position  of  the 
reticule  under  the  two  conditions  named.  This  is  the  spherical 
aberration. 

The  images  of  straight  lines  in  the  central  and  outer  zones  of  the 
field  are  sometimes  curved  either  inward  or  outward.  This  error, 
known  as  distortion,  should  be  smaU  in  any  service  telescope.  It 
may,  however,  be  greatly  increased,  especially  by  the  reversal  of  an 
objective  or  of  a  field  lens  of  an  eyepiece. 

Poorness  of  illumination  may  be  due  to  dirt  or  moisture  on  the 
surfaces  of  some  optical  element  or  in  rarer  cases  to  the  surface 
decomposition  of  the  glass  or  to  the  breaking  away  of  the  cement. 

The  condition  of  the  interior  surfaces  of  a  telescope  may  be  exam- 
ined without  removing  the  eyepiece  by  a  magnifying  glass  held  in 
rear  of  the  eyepiece  and  moved  to  bring  the  desired  surfaces  into  view. 

If  double  images  of  well-defined  lines  near  the  center  of  the  field 
appear  the  fault  is  probably  due  to  errors  in  the  roof  angle  of  the 
prisms. 

Errors  in  the  adjustment  of  prisms  may  be  detected  by  testing  the 
coUimation  ot  the  telescope, 

34.  Mounting  of  cross  wires. — Wires  are  mounted  on  a  frame  or 
holder  in  shallow  grooves.     Before  assembling  see  that  the  ends  of 


19 

these  grooves  are  free  from  sharp  edges.  Especially  see  that  the  end 
of  the  groove  from  which  the  wire  emerges  before  passing  imder  a 
clamp  is  slightly  rounded.  The  lower  surface  of  the  clamp  or  clip 
should  be  smooth  and  its  edges  slightly  rounded  to  avoid  cutting  the 
wire.  Unless  these  precautions  are  observed  in  mounting  cross  wires 
in  gun  sights,  the  wire  may  be  broken  by  the  shock  of  firing. 

In  moimting  platinum  wire  0.001  inch  in  diameter,  clamp  the  free 
end  of  the  wire  under  the  clamp  of  the  holder  in  line  with  the  slot. 
Place  a  weight  on  the  other  end  of  wire,  grasp  the  holder  with  one 
hand,  slide  the  wire  under  the  clamp,  guide  it  into  the  groove,  use  a 
slight  pressure  on  the  holder  to  draw  the  wire  taut,  and  then  clamp  the 
wire. 

35.  Platinum  wire  0.0005  inch  in  diameter  is  silver  coated.  To 
remove  the  silver  coating,  bend  a  U-shaped  frame  of  wire,  preferably 
aluminum,  of  y^  inch  or  smaller  diameter.  The  length  of  the  U  should 
be  about  3  inches  and  the  distance  between  prongs  J  inch  to  }  inch 
greater  than  the  length  of  cross  wire  required.  Cover  the  frame 
with  beeswax  for  a  distance  of  1  inch  from  the  open  end.  Mount 
the  wire  loosely  on  the  frame,  protecting  the  ends  by  the  wax.  Then 
hold  the  wire  mounted  on  the  frame  in  a  concentrated  solution  of 
nitric  acid  for  5  or  10  minutes.  Examine  it  carefully  with  a  magnify- 
ing glass  to  see  that  all  silver  has  been  removed.  Then  wash  by 
gently  moving  the  wire  through  water. 

The  wire,  still  mounted  on  the  frame,  should  be  slipped  under  the 
clamps  and  guided  into  the  grooves  of  the  holder.  Before  clamping 
bring  the  wire  taut  by  permitting  the  U  frame  to  be  supported  by 
the  wire.     After  clamping  cut  the  wire  from  the  frame. 

36.  In  mounting  wire  0.0005  inch  in  diameter  or  finer  without 
clamps,  use  a  solution  of  ordinary  brown  shellac  dissolved  in  alcohol 
to  the  consistency  of  cream.  FoUow  the  same  method  as  described 
above  except  that  after  the  wire  is  located  in  its  groove  apply  a  drop 
of  shellac  with  a  sharp  pointed  piece  of  wood  or  other  sharp  tool. 
Allow  the  shellac  to  dry  from  1  to  2  hours  before  cutting  the  wire  from 
the  frame. 

37.  Plastering  'prisms  in  their  holders. — ^After  adjusting  the  prism 
in  its  holder  for  collimation  of  the  horizontal  cross  wire,  set  up  the 
prism  adjusting  screws  lightly  and  set  the  lock  nut  for  the  prism 
adjusting  screw  against  the  holder.  Then  remove  the  holder  with 
the  prism  from  the  telescope  and  fiU  the  space  between  the  prism  and 
the  holder  with  plaster  of  paris  and  water  mixed  to  the  consistency  of 
thick  paste.  Work  the  plaster  in  the  space  between  the  prism  and 
holder,  using  a  knife,  piece  of  wood,  or  any  other  instrument,  pack 
the  plaster  tightly  and  completely  fiU  the  space.  Remove  the  sur- 
plus plaster  and  set  aside  to  harden  for  two  or  three  hours. 


20 

Use  a  good  grade  of  dental  plaster  of  paris,  which  will  set  in  from 
5  to  10  minutes.  ^ 

38.  Directions  for  preparing  a  silvering  paste  and  for  applying  it. — 
In  case  the  silvering  on  metallic  parts  of  instruments  becomes  worn 
and  unsightly,  a  moderately  thin  paste  should  be  made  by  mixing 
1  part  of  silver  chloride,  15  parts  of  cream  of  tartar,  and  5  parts  of 
salt  (NaCl)  and  enough  water  added  to  the  mixture  to  form  a  paste. 
Let  the  silver  stand  over  night  to  remove  impurities. 

Clean  the  surface  to  be  silvered  with  fine  emery  or  crocus  cloth. 
All  grease,  dirt,  etc.,  should  be  relnoved  in  order  to  get  good  results. 
Then  rub  the  surface  thoroughly  with  salt  and  a  little  water.  Apply 
the  paste  with  the  finger,  rubbing  until  a  good  white  surface  appears, 
then  wash  over  the  surface  with  cream  of  tartar  and  water.  Wipe 
the  surface  and  allow  to  stand  until  thoroughly  dry.  It  wiU  be 
preferable  if  the  silvered  surface  is  warmed  before  lacquering,  but  this 
may  be  found  impracticable  in  many  cases.  The  paste  should  be 
used  shortly  after  preparation.  - 

Then  lacquer  with  white  lacquer,  using  two  coats.  The  white 
lacquer  is  prepared  as  follows:  Dissolve  1  pound  of  kiln-dried  white 
shellac  in  one-half  gallon  of  alcohol,  allow  it  to  stand  24  hours,  then 
run  it  twice  through  filter  paper.  It  may  be  obtained  ready  for  use 
by  requisition  in  the  usual  manner. 

39.  LitJiarge  cement — The  litharge  cement  used  in  sealing  pano- 
ramic sights  is  manufactured  as  follows :  Boil  raw  linseed  oil  in  a  pan 
imtil  it  smokes.  Then  set  it  on  fire  and  let  it  burn  for  a  few  minutes. 
Cover  the  pan  to  extinguish  the  blaze  and  pour  while  warm  into  a 
receptacle  containing  red  lead  and  Mtharge  in  the  proportions  of  1 
oimce  of  each  to  a  quart  of  oil.  Keep  at  a  temperature  of  70°  F.  for 
10  days  and  agitate  once  a  day.  Apply  the  cement  in  a  thin  coating 
to  the  parts  to  be  cemented  and  aUow  it  to  dry  at  the  ordinary  tem- 
perature. Only  a  very  small  quantity  of  cement  is  required.  It 
dries  very  slowly.     It  is  not  affected  by  either  water  or  alcohol. 

This  cement  is  used  for  sealing  the  interior  chambers  of  instru- 
ments. To  obtain  a  sealed  joint,  careful  fitting  of  plane  surfaces  is 
required.  The  cement  wiU  not  compensate  for  poor  fitting.  Litharge 
cement  may  be  dissolved  by  turpentine. 

40.  Silvering  of  mirrors. — A  silvering  solution  may  be  prepared  as 
follows:  Make  separately  two  solutions — one  to  be  designated  solu- 
tion No.  1  and  the  other  solution  No.  2. 

Solution  No.  1.  Mix  49.6  grams  of  nitrate  of  silver  (dry  in  crystals) 
and  113.4  cubic  centimeters  of  distilled  water.  After  the  silver 
nitrate  has  been  dissolved,  add  ammonia  drop  by  drop  until  the 
brown  precipitate  falls.  Stop  adding  ammonia  just  before  the  solu- 
tion clears. 


21 

Solution  No.  2.  Mix  35.43  grams  of  Rochelle  salts  (dry  in  crystal) 
and  85.05  cubic  centimeters  of  distilled  water. 

Take  one  part  of  solution  No.  1,  one  part  solution  No.  2,  and  two 
parts  distilled  water  in  a  small  vessel  just  large  enough  to  hold  the 
piece  to  be  silvered.  First  carefully  clean  the  surfaces  to  be  silvered 
with  grain  alcohol.  Suspend  the  piece  in  the  vessel  with  the  face  to 
be  silvered  downward  and  immersed  a  httle  below  the  surface  of  the 
solution. 

Place  the  vessel  with  suspended  piece  on  a  receptacle  containing 
white  sand  and  heat  over  a  gas  flame  until  the  temperature  of  the 
solution  is  brought  nearly  to  the  boiling  point.  Extinguish  the 
flame  and  allow  to  cool.  When  cold  remove  the  silvered  piece  and 
wash  with  distilled  water.  Remove  any  superfluous  silvering  by 
rubbing  with  a  small  pine  stick  previously  wet  with  50  per  cent 
solution  of  nitric  acid.  Wash  the  piece  in  water  and  then  in  alcohol 
and  allow  to  dry  for  two  or  three  hours,  when  it  wiU  be  ready  for  a 
protecting  cover,  preferably  two  coats  of  shellac  varnish. 

For  large  mirrors  use  a  covering  of  paraflin  backed  with  tin  foil. 
The  mirror  is  gently  heated  and  the  melted  paraffin  is  poured  in  a  thin 
film  over  the  entire  silvered  surface.  For  large  mirrors  great  care 
must  be  taken  in  heating  the  mirror  and  in  applying  the  hot  paraffin, 
as  extremes  of  temperature  may  cause  the  glass  to  crack  after  the 
paraffin  has  flowed  evenly  over  the  entire  silvered  surface  and  the  tin- 
foil backing  is  applied.  The  paraffin  prevents  the  action  of  the 
atmosphere  on  the  silvered  surfaces  and  the  tin-foil  backing  prevents 
the  paraffin  from  being  rubbed  or  scratched  off.  For  small  work,  as, 
for  instance,  the  prisms  of  the  Weldon  range  finders,  however,  either 
of  the  following  mixtures  may  be  used: 

(a)  A  mixture  of  beeswax  and  resin — equal  parts.  The  beeswax 
is  sliced  in  small  pieces  and  boiled  so  as  to  get  rid  of  aU  free  acid, 
and  the  resin  is  selected  as  pure  as  possible.  The  mixture  is  put  on 
quite  hot.  It  is  well  to  have  the  prisms  warm  before  applying  the 
mixture. 

(h)  The  method  given  in  (a)  may  be  improved  upon  by  uging  the 
best  shellac,  if  this  can  be  obtained  free  from  impurities.  Shellac 
may  be  prepared  by  dissolving  out  the  impurities  in  absolute  alcohol, 
which  should  not  contain  more  than  0.2  per  cent  of  water.  After 
dissolving,  filter  the  varnish  through  three  thicknesses  of  cheese- 
cloth. After  silvering,  heat  the  prisms  to  about  160°  F.  and  apply 
two  coats  of  varnish. 

41.  Cementing  of  optical  elements. — When  the  conditions  described 
in  paragraph  28  become  sufficiently  pronoimced  to  obscure  the  image, 
the  lenses  of  prisms  affected  should  be  removed  and  placed  in  an 
alcohol  bath  to  dissolve  out  the  balsam.  It  frequently  takes  from 
two  days  to  two  weeks,  or  over,  to  separate  the  parts  of  lenses.     In 


22 

refractory  cases  the  alcohol  may  be  heated  gradually  over  a  water 
bath  at  150°  F.  to  accelerate  the  operation.  The  parts  should  not 
be  removed  from  a  hot  bath,  but  should  be  left  to  cool  off  gradually. 
After  separating  the  parts,  remove  all  trace  of  the  old  balsam  and  clean 
and  dry  thoroughly  preparatory  to  recementing.  Absolute  cleanli- 
ness of  the  surface  is  necessary.  The  room  in  which  the  operation  is 
conducted  should  be  as  free  from  dust  as  possible.  The  balsam  should 
always  be  the  best  obtainable  quality  of  paper-filtered  Canada 
balsam.  In  cementing,  spread  a  thin  film  of  balsam  over  the  sur- 
faces to  be  cemented;  be  sure  that  the  film  entirely  covers  each 
surface  and  that  no  air  bubbles  occur,  then  bring  the  parts  carefully 
together  and  place  in  a  receptacle  free  from  dust  for  the  preliminary 
setting.  By  the  preliminary  setting  is  meant  the  first  stage  of  the 
cementing  process,  in  which  the  balsam  gradually  draws  the  two  sur- 
faces closer  and  closer  together  and  holds  them  fairly  tight,  but  still 
adjustable.  The  time  for  the  preliminary  setting  varies  from  one  to 
two  days,  the  interval  being  less  as  the  temperature  increases.  When 
it  is  found  by  actual  trying  that  the  surfaces  are  held  fairly  tight 
together,  the  final  close  adjustment  by  hand  should  be  made.  For 
lenses,  this  consists  in  getting  the  mechanical  and  optical  axes  of  the 
group  into  coincidence. 

42.  Cementing  lenses. — Compound  lenses  when  issueil  in  instru- 
ments have  already  been  properly  assembled.  Before  separating 
such  lenses,  therefore,  a  soft-pencil  arrow  (y\)  should  be  placed  across 
the  circumferential  rim  of  the  lenses,  crossing  aU  in  the  direction  of 
the  optical  axis.  This  pencil  arrow  should  be  carefully  preserved,  for 
in  reassembling  these  same  lenses,  if  the  pencil  mark  on  each  letis  is 
brought  into  proper  relation  with  the  marks  on  the  other  lenses,  the 
original  relative  position  will  be  exactly  reproduced.  If  for  any 
reason  one  part  of  the  group  has  had  to  be  changed  the  entire  group 
will  have  to  be  tested  again  for  correct  relation  and  then  assembled. 

To  determine  whether  the  lenses  of  a  group  are  properly  ground 
for  assembhng,  take  them  carefully  by  the  rims  and  assemble 
them  without  balsam  in  the  position  which  they  should  occupy. 
For  properly  ground  surfaces,  a  series  of  color  rings  symmetrically 
placed  about  the  optical  axis  will  be  observed  when  two  adjoining 
lenses  of  a  group  are  brought  together.  Should  the  surfaces,  how- 
ever, be  too  high  or  too  low  in  spots,  then  at  these  spots  either  absence 
of  color  rings,  or  color  rings  appearing  which  have  their  center  out 
of  the  optical  axis  of  the  group,  will  be  observed,  depending  on  the 
extent  of  the  incorrect  surface.  When  this  color  test  shows  the  sur- 
faces are  not  in  proper  contact,  the  parts  should  be  returned  for 
regrinding  and  repolishing.  Where  good  results  are  obtained,  the 
best  position  should  be  marked  with  an  arrow  (y\)  across  the  rim 
and  the  group  then  assembled  with  balsam. 


23 

43.  Cementing  prisms. — Compound  prisms  are  more  difficult  to 
cement  than  lenses.  For  prisms  a  target  must  be  constructed  and  a 
fixture  for  holding  the  prisms  during  adjustment  must  be  arranged, 
depending  on  the  shapes  of  the  prisms.  In  preparing  fixtures  or  in 
inserting  prisms  into  the  fixtures  do  not  scratch  the  glass.  All  grit, 
chips,  and  dirt  must  be  carefully  avoided. 

The  following  method  should  be  followed  in  adjusting  and  as- 
sembling the  parts  of  a  Brashear-Hastings  erecting  prism,  assum- 
ing that  each  of  the  parts  is  correct  in  itself:  Consult  first  the  draw- 
ings of  the  instrument  to  which  the  prism  belongs,  and  determine 
from  them  the  amount  of  overhang  each  of  the  30°  prisms  has  over 
the  ends  of  the  90°  prism.  Cement  the  two  30°  prisms  to  the  90° 
prism  with  balsam,  taking  care  to  get  each  in  the  proper  relation  as 
to  overhang,  parallelism  of  sides,  etc.  Then  put  the  group  aside  for 
the  balsam  to  set.  As  the  balsam  sets  it  gradually  draws  the  prism 
surfaces  closer  and  closer  together.  After  a  few  days  (one  or  two 
if  the  process  is  aided  by  gentle  baking  in  a  properly  constructed 
oven)  it  will  be  foimd  that  the  prisms  require  a  little  effort  to'move 
them  from  one  position  to  another.  This  is  the  time  for  final  adjust- 
ment. Place  the  prisms,  90°  prism  down,  in  a  previously  prepared 
Y-shaped  steel  block,  of  which  the  sides  of  the  Y  make  an  exact 
right  angle,  carefully  cut  and  ground  to  receive  the  90°  prism.  The 
lowest  element  of  the  Y  in  the  block  should  be  so  placed  as  to  make 
the  upper  plane  surface  of  the  90°  prism,  on  which  the  two  30° 
prisms  are  assembled,  horizontal  when  the  block  is  placed  in  a  hori- 
zontal position.  Place  a  target  containing  fine  vertical  and  hori- 
zontal axes  at  a  convenient  distance  (20  to  30  feet)  and  at  a  height 
corresponding  to  the  height  of  the  center  of  the  30°  prisms,  when 
the  entire  group  is  placed  in  the  Y  block.  Adjust  a  coUimating 
telescope  or  some  proper  mount  behind  the  Y  block,  so  that  when 
the  telescope  is  horizontal  in  looking  through  the  telescope  at  the 
axes  of  the  target,  the  prism  being  temporarily  removed  from  the 
Y  block,  the  cross  hairs  of  the  telescope  shall  coincide  with  the  axes 
of  the  target.  Now  place  the  Brashear-Hastings  prism  in  the  Y 
block  and  look  through  the  telescope  at  the  axes  of  the  target.  In 
the  general  case  the  cross  hairs  of  the  telescope  and  the  axes  of  the 
target  will  not  coincide.  To  bring  about  coincidence  move  the  Y 
block  carefully  on  its  horizontal  plate  until  the  axes  of  the  target  as 
seen  through  the  prism  coincide  with  the  cross  hairs  of  the  telescope. 
Having  attained  this  position,  be  sure  that  the  Y  block  and  the 
telescope  are  not  altered  in  position  during  the  subsequent  opera- 
tions. Now  lift  the  Brashear-Hastings  prism  out  of  the  Y  block  and 
tiu-n  it  180°  in  a  horizontal  plane  and  replace  in  the  Y  block.  This 
wiU  result  in  bringing  what  originally  had  been  the  far  30°  prism 


24 

next  to  the  telescope  and  in  moving  the  30°  prism  that  had  been 
next  to  the  telescope  to  the  target  side.  Again  look  through  the 
telescope.  If  the  prisms  are  correctly  adjusted  the  axes  of  the 
target  as  seen  through  the  prisms  in  their  new  position  will  still 
coincide  with  the  cross  hairs  of  the  telescope.  If  the  axes  and  cross 
hairs  do  not  coincide,  correct  for  half  the  error  by  moving  each  of  the 
30°  prisms  equal  amounts.  Correct  for  the  remaining  half  error  by 
moving  the  block.  Note  that  in  moving  the  30°  prisms  the  position 
of  these  prisms,  overhang,  parallelism  of  sides,  central  distance,  etc., 
remain  as  laid  down  in  the  drawings.  Having  obtained  coincidence 
by  the  methods  just  outlined,  reverse  the  prism  again  .and  continue 
correcting  for  half  the  observed  error  by  moving  the  prisms  and  for 
the  other  half  by  moving  the  block,  until  the  axes  and  cross  hairs  do 
not  lose  coincidence  after  reversing  the  prisms.  The  prisms  are  now 
adjusted  and  should  be  put  aside  to  allow  the  balsam  fully  to  set. 
After  the  balsam  has  fully  set,  the  small  end  pieces  should  be  cemented 
to  the  group  and  the  group  then  assembled  in  the  prism  holder  and 
then  in  the  optical  tube,  as  described  in  connection  with  special 
instruments,  the  adjustments  of  which  are  given  in  this  pamphlet. 

44.  Illumination  of  reticule. — The  intensity  of  illumination  of 
reticides  is  varied  by  withdrawing  the  lamp  from  the  aperture  which 
admits  the  entrance  cone  of  rays  to  the  reticule  chamber,  as  in  the  case 
of  the  azimuth  instrument  models  of  1900  and  1900  Mi,  or  by  varying 
the  diameter  of  the  entrance  cone  of  rays  by  means  of  a  fixed  and 
movable  diaphragm,  as  in  the  case  of  the  telescope  for  all  models  of 
depression  position  finders  and  2-inch  and  3-inch  telescopic  sights. 
In  order  not  to  obscure  the  field  of  view  the  intensity  of  illumi- 
nation of  the  reticule  should  be  reduced  as  much  as  possible  on  both 
the  horizontal  and  vertical  wires.  For  the  2-inch  and  3-inch  tele- 
scopes but  one  lamp  is  provided,  and  in  order  to  reduce  the  amount 
of  light  entering  the  reticule  chamber,  the  lower  mirror  on  the  lamp 
bracket  (see  paragraph  10,  pamphlets  Nos.  1955  and  1956)  should  be 
rotated  to  secure  the  maximum  intensity  of  illumination  and  the 
upper  mirror  should  be  rotated  to  secure  an  equal  degree  of  illumina- 
tion. The  intensity  of  illumination  of  both  wires  should  then  be 
reduced  as  much  as  possible  by  turning  the  finger  grip  which  operates 
the  moving  diaphragm. 

Mirrors  are  used  in  the  reticule  illumination  devices  of  the  tele- 
scopes of  the  Lewis  depression  position  finder  Type  A  and  the  2 -inch 
and  3-inch  telescopic  sights.  In  case  the  necessary  intensity  of 
illumination  can  not  be  secured,  the  mirror  holders  should  be  removed 
and  the  mirrors  polished  with  a  dry  cloth. 

For  night  observation  the  best  results  will  be  obtained  by  the 
use  of  the  low-power  eyepiece  furnished  with  instruments.      The 


25 

diameter  of  the  eye  ring  is  greater  with  the  low-power  eyepieces 
and  more  nearly  equals  that  of  the  pupil  of  the  eye.  Hence  the 
field  of  view  is  better  illuminated. 

45.  The  following  examples  are  given  as  directions  for  removal  of 
optical  parts,  for  cleaning,  and  for  readjusting.  The  methods  of 
making  adjustments,  etc.,  will  not  be  described  for  all  instruments, 
but  only  for  the  various  types  of  instruments. 

TELESCOPIC   SIGHT,  MODEL   OF   1899. 
(See  Handbook  of  Sights  for  Cannon  and  Drawings  15-2A22,  1,  2,  and  3.) 

46.  To  remove  the  erecting  system. — Remove  the  objective  and  cell, 
the  erecting  system  clamp  ring  screw,  the  tube  cap,  deflection  slide, 
and  lower  deflection  scale.  Enter  teat  wrench  No.  29  through  the 
objective  end  of  telescope,  engage  it  in  the  teat  holes  in  the  first 
diaphragm  and  screw  the  erecting  system  completely  out  through 
the  eyepiece  end  of  telescope. 

Scratch  a  short  line  across  all  joints  as  an  aid  in  assembling  each 
piece  in  the  correct  order  and  in  tightening  up  screw  threads.  Some 
of  the  parts  have  similar  threads  on  both  ends  and  care  must  be  taken 
not  to  reverse  the  piece  end  for  end.  Do  not  remove  any  lens  from 
its  cell. 

Unscrew  the  first  lens  cell.  Do  not  remove  the  first  diaphragm. 
Grasp  the  erecting  system  in  a  chuck  and  unscrew  the  second  lens 
cell.  Clean  and  replace  both  cells.  Remove  the  third  lens  cell, 
clean,  and  reassemble. 

47.  To  assemble  the  erecting  system. — Insert  the  erecting  system 
threaded  and  rearmost,  through  the  reticule  chamber  and  screw  into 
place,  using  teat  wrench  No.  29.  Align  the  hole  in  the  wall  of  the 
front  erecting  system  tube  with  the  seat  of  erecting^  system  clamp 
ring  screw.  Assemble  the  objective,  the  reticule,  and  the  eyepiece 
and  test  to  determine  whether  parallax  can  be  removed  from  the 
cross  wires.  If  not,  remove  the  objective  and  revolve  the  erecting 
system  tube  in  the  proper  direction  until  parallax  may  be  removed 
and  the  clamp  ring  screw  assembled.  Replace  erecting  system 
clamp  ring  screw. 

Little  dirt  works  into  the  erecting  system  of  this  telescope.  It  will 
not  therefore  be  necessary  to  remove  the  erecting  system  except  at 
long  intervals. 

48.  To  collimate  the  telescope. — ^Mount  bracket  No.  102  of  optical 
repair  kit  on  fixture  No.  86,  and  pedestal  No.  85.  Level  the  pedestal. 
Insert  collimating  telescope  No.  98  in  bracket  No.  102  and  bring  the 
image  of  the  crosslines  of  a  target  into  coincidence  with  the  reticule 
to  collimating  telescope.  Test  the  collimation  of  the  collimating 
telescope  and  correct  it  if  necessary.     Then  remove  bracket  No.  102 


26 

and  collimatijig  telescope  from  fixture  No.  86  and  place  the  telescope 
to  be  coUimated  upon  the  fixture  without  changing  the  position  or 
adjustment  of  fixture.  Loosen  the  four  reticule  holder  screws  and 
adjust  reticule  holder  so  that  the  horizontal  wire  coincides  with 
horizontal  wire  of  target  and  so  that  the  vertical  wire  is  plumb. 
Turn  the  deflection  kaob  until  vertical  wire  coincides  with  vertical 
line  of  target.  Loosen  the  upper  deflection  scale  screw^s  and  reset 
the  upper  deflection  scale  if  necessary.  Loosen  the  two  deflection 
knob  screws  and  set  the  deflection  micrometer  to  0.  Reset  the 
lower  deflection  scale  and  test  adjustment  by  the  eyepiece. 

This  telescope  may  also  be  collimated  by  using  bracket  No.  102 
on  the  telescope  seat  of  the  gun  carriage.  The  method  of  adjusting 
is  the  same  as  described  above.  Collimating  the  telescope  on  the 
gun  carriage  will  probably  be  found  preferable. 

TELESCOPES   WITH   BRASHEAR-HASTINGS   ERECTING  PRISMS. 

49.  The  telescopes  of  the  following  instruments  are  equipped  with 
this  kind  of  prisms: 

Telescopic  sight,  models  of  1896  Mi,  1897,  1898,  1898  M,  and  1902. 
Lewis  depression  position  finder,  types  A  and  B. 
Swasey  depression  position  finder,  type  A.  t 

Azimuth  instrument,  model  of  1900.  *■ 

Three-inch  telescopic  sight,  model  of  1904,  Nos.  1-26,  inclusive. 


TELESCOPIC   SIGHTS,  MODELS   OF  1896   MI,  1897,  1898,  AND   1899  M. 
(See  Handbook  of  Sights  for  Cannon  and  Drawings  15-2A19,  1  to  4,  inclusive.) 


50.  For  adjusting  telescopic  sights,  models  of  1896  Mi,  1897, 
1898,  and  1898  M,  a  trunnion  bracket  (No.  87)  is  furnished  with  the 
optical  repair  kit.  The  following  examples  of  its  use  will  be  given, 
which  is  applicable  to  either  of  these  models  of  sights.  Attention  is 
also  invited  to  ' '  Handbook  of  Sights  for  Field  and  Seacoast  Carriages 
not  covered  by  other  Pamphlets"  (Form  No.  1952).  The  fixtures 
and  tools  mentioned  by  numbers  pertain  to  the  optical  repair  kit. 

51.  Prepare  a  target  on  which  is  one  horizontal  line  and  two  ver- 
tical lines,  the  distance  between  which  is  equal  to  twice  the  horizontal 
distance  from  the  axis  of  the  telescope  to  the  axis  of  the  telescope 
trunnions.  The  horizontal  line  of  target  should  lie  as  near  as  prac- 
ticable to  the  horizontal  plane  which  includes  the  optical  axis  of  the 
telescope.  One  leveling  screw  of  the  pedestal  should  lie  in  the  ver- 
tical plane  of  the  trunnions  of  the  sight. 

Level  the  trunnion  bracket  (Fixture  No.  87)  in  the  pedestal  (Fix- 
ture No.  85)  with  a  striding  level  (No.  74).  Set  the  telescope  without 
the  prisms  assembled  in  the  trunnion  bracket;  adjust  the  telescope 
level  to  make  the  bubble  central  in  level  vial  by  changing  the  elevation 


27 

of  the  telescope.  Set  the  micrometer  elevation  dial  and  vernier  to 
read  0.  (The  setting  of  level  should  be  tested  in  the  usual  way.) 
Insert  the  cross-wire  frame  (if  not  already  assembled)  and  adjust 
the  horizontal  wire  to  coincide  with  the  horizontal  line  on  the  target. 
Remove  the  telescope  from  the  fixture.  Rotate  the  swivel  of  trun- 
nion bracket  180°  from  its  former  position  against  the  stop.  Replace 
the  telescope  in  the  bracket  bottom  side  up.  If  the  horizontal  cross 
wire  is  not  in  the  plane  of  the  optical  axis,  correct  for  half  the  error 
by  moving  the  cross-wire  frame  by  the  small  adjusting  screws  in  the 
top  of  the  frame,  and  for  half  the  error  by  moving  that  leveling  screw 
of  the  pedestal  which  lies  in  the  same  vertical  plane  as  the  axis  of  the 
trunnions  of  the  sight;  without  changing  the  level  of  the  pedestal, 
reverse  the  telescope  and  recorrect  if  necessary. 

52.  If  the  horizontal  cross  wire  can  not  be  adjusted  due  to  error 
in  adjustment  of  the  telescope  level,^  the  cross-wire  frame  should  be 
left  in  an  intermediate  position  and  the  adjustment  for  coUimation 
made  as  closely  as  practicable  by  adjusting  the  prisms  (see  below) 
and  corrected  as  described  above  after  the  prisms  are  adjusted. 

53.  For  adjusting  the  vertical  cross  wire  move  the  vertical  wire" 
to  near  the  center  of  the  diaphragm  and  the  micrometer  deflection 
dial  to  zero  for  trial.  (It  is  assumed  that  the  prisms  are  disassembled.) 
Put  the  telescope  in  the  bracket.  First  adjust  the  cross  level  so  that 
the  bubble  of  level  vial  remains  central  throughout  the  entire  arc 
of  elevation  of  the  telescope  (for  the  models  of  1898  and  1898  M 
sights).  If  adjustment  of  the  level  vial  is  necessary,  remove  the  cap 
from  cross  level  and  adjust  it  by  the  internal  adjusting  screws  (see 
paragraph  172).  If  the  adjustment  is  made  correctly,  the  vertical 
cross  wire  should  foUow  a  plumb  line  during  elevation  of  the  telescope. 

54.  In  adjusting  the  cross  levels  of  the  models  of  1896  Mi  and 
1897  sights,  set  the  telescopic  sight  tnmnions  approximately  level  in 
the  trunnion  bracket  and  the  cross  wire  at  0°  deflection  and  level  the 
cross  level.  Align  the  vertical  wire  on  a  plumb  line  without  changing 
the  deflection  setting.  Then  elevate  the  telescope  through  the  great- 
est possible  range  of  elevation  scale.  If  the  vertical  wire  does  not 
follow  the  plumb  line,  correct  the  error  by  the  adjusting  screw  of  the 
telescopic  sight  holder  to  bring  the  vertical  wire  into  coincidence  with 
the  plumb  line.  Then  adjust  the  cross  level  by  moving  its  axis  in  a 
plane  perpendicular  to  the  surface  of  the  base  of  the  level  case  imtil 
the  bubble  is  central.     Repeat  the  test  to  verify  the  setting. 

Then  put  the  sight  in  the  trunnion  bracket  of  gun  at  0°  elevation 
and  level  the  cross  level.  Elevate  the  gun  through  as  great  an  arc  as 
possible.  If  the  bubble  of  cross  level  does  not  remain  central,  slightly 
loosen  the  screws  of  the  level  case  and  adjust  the  level  so  that  the 
bubble  is  central  at  this  position.     In  this  adjustment  the  axis  of  the 


28 

level  is  moved  in  a  plane  parallel  to  the  base  of  the  level  case.  Kepeat 
test  and  after  adjustment  is  satisfactory,  readjust  the  level  for  move- 
ment of  telescope  in  elevation  as  directed  in  preceding  paragraph. 

55.  After  the  cross  level  is  adjusted' ahgn  the  telescope  on  the 
right-hand  vertical  line  of  target.  Take  out  the  telescope  and  replace 
it  bottom  side  up,  turning  the  swivel  of  bracket  as  before.  If  the 
vertical  wire  does  not  coincide  with  the  left-hand  vertical  line  of 
target,  determine  the  amount  of  the  error  by  means  of  the  microme- 
ter deflection  dial,  and  turn  back  the  micrometer  toward  the  first 
position  by  one-half  of  the  measured  error.  Reset  the  telescope  on 
the  target,  with  the  vertical  wire  in  this  new  position.  Reverse  the 
telescope  and  proceed  as  before  to  correct  the  adjustment  of  the 
vertical  wire.  The  micrometer  deflection  dial  should  be  set  at  0 
and  the  internal  scale  adjusted  for  this  position. 

56.  CoUimate  the  prisms  as  described  below  for  3-inch  telescopic 
sights,  model  of  1904,  Nos.  1-26,  inclusive.  Then  remove  prism  and 
holder  from  the  telescope  tube,  fill  the  space  around  the  two  adjust- 
ing screws  between  the  prism  and  the  holder  with  plaster  of  paris 
and  allow  the  plaster  to  set.  Carefully  clean  the  prisms  and  replace 
them  and  the  holder  in  the  telescope.  Set  the  telescope  with  the  ver- 
tical cross  wire  on  a  vertical  fine  of  target.  Insert  the  holder  screws 
into  the  telescope  body  and  align  the  prism  holder  so  that  the  coin- 
cidence of  the  vertical  cross  wire  with  a  line  on  the  target  is  not  dis- 
turbed. Test  the  adjustment  by  reversing  the  telescope  as  described 
above.  Then  tighten  the  prism  holder  screws  and  replace  the  prism 
box  cover.  The  horizontal  and  vertical  axis  should  then  be  tested 
for  collimation  and  coUimated  if  necessary,  as  described  above. 

57.  After  a  workman  has  become  famihar  with  the  adjustment 
of  sights  in  the  manner  described  above,  it  will  be  sufficient  if  prisms 
are  located  centrally  in  telescope  tube  before  the  cross  wires  are 
collimated.  Then  set  the  horizontal  cross  wire  in  an  intermediate 
position  and  coUimate  by  adjusting  the  screws  between  the  prism 
and  holder,  moving  the  axis  of  the  prisms  in  a  vertical  plane  only. 
Remove  the  prism  and  the  holder  and  fill  the  space  between  them 
with  plaster  of  paris.  Then  complete  the  coUimation  of  the  hori- 
zontal wire  by  adjusting  the  cross-wire  frame.  Adjust  the  vertical 
wire  as  described  above.  In  this  case,  test  the  location  of  prisms  in 
the  tube  by  looking  through  the  telescope  and  observing  that  neither 
edge  of  prism  is  seen  within  the  diaphragm  or  that  both  edges  are 
seen  equally  spaced  from  the  sides  of  diaphragm. 

58.  After  a  telescopic  sight  is  adjusted  in  this  manner,  it  should 
be  tested  for  parallelism  with  the  axis  of  the  bore  of  the  gun.  If  the 
line  of  coUimation  of  the  sight  is  not  parallel  with  the  axis  of  the  bore 
at  0°  deflection  and  0°  elevation,  the  sight  brackets  on  the  gun  car- 


29 

riage  should  be  adjusted,  or  tlie  V's  of  the  trunnion  bracket  should  be 
filed  or  scraped  to  make  the  line  of  collimation  parallel  to  the  axis  of 
the  bore  under  the  conditions  stated. 

TELLESCOPIC   SIGHT,   MODEL   OF   1902. 
(See  Drawings  15-2A18,  1,  2,  and  3.) 

59.  To  collimate  this  telescope,  use  collimating  telescope  No.  98 
with  rings  Nos.  101,  pertaining  to  the  optical  repair  kit,  in  the  cradle 
of  sight.  Point  the  gun  at  a  given  object  and  adjust  the  prisms  by 
the  prism-adjusting  screws  so  that  the  line  of  collimation  of  sight 
agrees  with  that  of  coUimating  telescope.  The  erecting  prism  holder 
is  located  in  the  telescope  tube  by  dowel  pins.  Relocation  of  these 
pins  will  not  be  required  except  to  compensate  for  errors  in  cementing 
the  elements  of  the  erecting  prism.  After  adjustment  of  the  hori- 
zontal plane  containing  the  line  of  collimation,  set  up  the  prism- 
adjusting  screws  so  that  they  just  come  in  contact  with  the  glass 
surface,  set  the  lock  nuts  and  fill  in  with  plaster  of  paris  as  described 
in  paragraph  37  above. 

3-INCH  TELESCOPIC  SIGHTS,  MODEL  1904,  NOS.  1-26,  INCLUSIVE. 

(See  Plate  A.) 

60.  To  dismount  the  eyepiece  and  prism. — To  remove  the  prism 
holder,  unscrew  the  four  screws  (1)  on  cover  (2);  unscrew  (3)  and 
lay  aside  with  washer  (4);  unscrew  (5),  and  the  whole  prism,  with 
holder,  can  be  taken  from  the  telescope  body.  To  remove  the  prism 
from  its  holder,  unscrew  (6),  take  out  piece  (7),  and  the  whole  prism 
is  now  ready  to  be  removed.  Great  care  must  be  taken  to  replace 
the  prism  in  exactly  the  same  position  in  the  holder.  Plate  A  shows 
clearly  the  method  of  dismounting  the  eyepiece.  No  attempt  should 
be  made  to  remove  the  lenses  of  the  eyepiece  from  their  cells. 

61.  The  lenses  of  the  objective  of  this  telescope  are  secured  in  the 
holder  by  crimping,  and  should  not  be  removed  for  cleaning  or  any 
other  purpose,  except  by  an  expert  instnunent  maker. 

62.  To  assemble  and  adjust  the  telescope. — ^Assemble  and  insert  the 
eyepiece,  but  not  the  prism,  as  the  telescope  must  be  adjusted  without 
the  latter.  Place  the  coUimating  telescope  No.  98,  using  rings 
No.  103  in  the  telescope  bearings  of  the  sight  cradle.  Select  a  target 
at  least  300  yards'  distance  and  bisect  it  with  the  cross  wire.  Then 
revolve  the  collimating  telescope  180°,  and  if  the  cross  wires  bisect 
the  same  target  exactly  then  the  adjustment  of  the  coUimating  tele- 
scope is  correct. ,  Remove  the  coUimating  telescope  and  without 
changing  the  pointing  of  the  sight,  insert  the  3''  telescope  in  its  bear- 
ing in  the  cradle.     If  the  cross  wires  are  to  one  side,  or  up  or  down 


30 

from  the  target  selected,  then  the  whole  error  must  be  corrected  with 
the  cross-wire  adjusting  screws  (9).  Check  the  correctness  of  the 
adjustment.  Then  with  the  telescope  in  position  and  carefully 
ahgned  on  the  target,  insert  the  prism  and  screw  down  tight  screw 
(5)  and  also  screw  (3).  If  the  telescope  does  not  bisect  the  target 
exactly  as  before,  then  the  correction  up  or  down  must  be  made 
wholly  with  the  screws  (3)  and  (10);  (3)  holds  the  prism  holder  to 
the  telescope  body,  and  (10)  are  pushing  screws,  which  raise  and  lower 
the  image  of  the  objective  in  relation  to  the  cross  wires.  The  adjust- 
ing sideways  is  done  by  screws  (11),  and  to  do  this  the  screw  (3) 
must  be  unscrewed  and  the  whole  prism  holder,  with  the  prism  hinged 
on  screw  (5),  raised  enough  to  reach  the  screws  (11)  and  then  dropped. 

Great  care  must  be  taken  that  both  the  screws  (10)  are  turned 
exactly  the  same  amount  and  touch  the  telescope  body  at  the  same 
time,  otherwise,  by  screwing  down  the  screw  (3),  the  whole  holder 
will  be  twisted  and  the  prism  may  be  broken  or  strained  sufficiently 
to  destroy  good  definition. 

After  inserting  and  adjusting  the  prism,  the  telescope  should  point 
to  exactly  the  same  point  as  without  the  prism.  All  adjusting  with 
screws  must  be  done  carefully  and  in  such  a  way  as  not  to  put  any 
strain  on  the  metal,  because  if  the  screws  are  too  tight  the  adjustment 
wiU  change  rapidly.  As  a  general  rule,  it  is  always  advisable  to 
tighten  each  screw  just  enough  to  secure  a  firm  contact  between 
the  two  parts  without  any  strain  whatever. 

SWASEY   DEPRESSION   POSITION   FINDER,    TYPE   A. 
(See  Plates  B  and  C.) 

63.  To  dismount  the  eyepiece. — Plate  C  indicates  clearly  the  con- 
struction and  method  of  dismounting  the  eyepiece.  No  attempt 
should  be  made  to  remove  the  lenses  of  the  eyepiece  from  their  rings. 

64.  To  dismount  the  objective  (Plate  C). — Unscrew  objective  shade 
(45-46),  then  unscrew  the  objective  cell  (91),  unscrew  the  ring  (93) 
which  holds  the  objective  in  the  cell,  and  put  a  clean  piece  of  hnen 
on  a  table  and  take  out  the  objective  (92)  from  the  cell  (91).  To 
do  this  it  is  best  to  unscrew  first  ring  (93)  and  lay  the  cell  of  the 
table  with  the  ring  (93)  end  up.  Then  put  a  clean  piece  of  linen 
over  the  left  hand;  put  left  hand  covered  with  hnen  on  top  of  cell 
and  lenses,  and  reverse,  so  that  the  left  hand  is  on  the  bottom  and  the 
right  hand  on  the  top.  Now  raise  the  cell  slowly  and  both  lenses  will 
come  out  of  the  cell  easily.  Should  the  lenses  fit  a  httle  snugly,  es- 
pecially in  cold  weather,  bring  the  whole  cell  into  a  warm  room  and  let 
it  stand  for  about  one  hour;  the  lenses  should  then  be  readily  removed 
from  the  cell.  Before  separating  the  lenses,  place  a  soft-pencil  arrow 
(^)  across  the  circumference.    Clean  carefully  and  put  back  in  the 


31 

same  position.  There  are  three  small  pieces  of  paper  pasted  on  one 
of  the  lenses  of  the  objective,  exactly  120°  apart  and  at  the  egde,  to 
separate  the  two  lenses. 

65.  To  dismount,  re'place,  and  readjust  'prism  (Plate  B). — Remove 
cover  by  unscrewing  the  screws. 

Unscrew  the  two  screws  (1)  and  take  out  the  prism  with  its  holder, 
loosen  (4)  a  trifle,  take  out  screws  (2),  and  remove  crossbar  (3). 
Then  the  prisms  will  come  off  from  the  holder  easily. 

Clean  prisms  carefully,  insert  in  holder,  put  in  place  piece  (3);  put 
in  screw  (2)  and  tighten  screws  (3);  then  slowly  tighten  screws  (4). 

This  telescope,  with  the  Brashear-Hastings  prism  removed,  is  ad- 
justed exactly  as  described  for  the  telescope  of  Type  Ai  below. 
After  this  is  done,  the  Brashear-Hastings  prism  must  be  inserted  with 
screws  (1),  Plate  B,  and  if  the  image  now  on  the  target  is  too  high  or 
too  low,  then  this  must  be  corrected  with  screws  (4)  by  loosening  one 
screw  a  trifle  and  tightening  the  other  one.  If  the  image  is  to  one 
side,  loosen  slightly  one  of  the  screws  (1)  and  move  prism  holder  in 
desired  direction.  This  is  best  done  by  wedging  a  screw  driver  be- 
tween the  opening  of  the  telescope  body  and  the  prism  frame.  In 
case  the  prism  holder  can  not  be  moved  to  one  side  correct  the  error 
by  changing  the  collimation  of  the  objective.  After  adjusting,  put 
the  cover  on  top  of  the  telescope  and  secure  with  screws  (5). 

In  this  telescope  no  adjustment  of  the  reticule  is  provided. 

ADJUSTMENT    OF    PRISMS    OF    LEWIS    DEPRESSION    POSITION    FINDER, 

TYPE   A. 

(See  Pamphlet  No.  1873.) 

66.  The  vertical  adjustment  of  the  prisms  of  the  Type  A  position 
finder  should  be  made  in  reference  to  the  tide  scale  in  order  to  mini- 
mize, the  error  of  the  range  scale  for  various  heights  of  tide.  In 
making  this  adjustment,  set  the  range  scale  at  infinity  (if  not  prac- 
ticable set  at  maximum  range  on  scale)  and  the  tide  slide  at  either 
extreme  of  the  scale.  Set  up  a  target  with  horizontal  line  in  the 
horizontal  plane  of  the  axis  of  the  trunnions  of  telescope.  Direct  the 
telescope  on  the  target  and  by  turning  the  refraction  screw  bring  the 
horizontal  cross  wire  of  the  telescope  to  coincide  with  the  horizontal 
line  of  the  target.  Then  translate  the  tide  slide  to  the  other  extreme 
end  of  the  scale.  If  the  horizontal  cross  wire  stiU  remains  on  the 
horizontal  fine  of  the  target,  the  prism  is  correctly  adjusted  vertically. 
If  the  coincidence  of  the  cross  wire  and  the  horizontal  fine  is  disturbed, 
correct  half  the  error  by  rotating  the  prisms  in  a  vertical  plane  by 
means  of  the  prism  holder  screws  and  half  the  error  by  rotating  the 
telescope  on  the  trunnions  by  the  refraction  screw.  Repeat  until  the 
adjustment  is  found  to  be  correct. 


32 

67.  In  the  telescopes  for  the  followmg  instruments  Porro  prisms 
are  used  for  erecting  the  image : 

Swasey  depression  position  finder,  type  All. 

Lewis  depression  position  finder,  model  of  1907. 

Azimuth  instrument,  models  of  1900  Mi  and  1910. 

Three-inch  telescopic  sight,  models  of  1904  (after  No.  26)  and  1910. 

Two-inch  telescopic  sight,  models  of  1906  and  1909. 

Observation  telescope,  seacoast,  model  of  1908. 

Observation  telescope,  field,  model  of  1908. 

Battery  commander's  telescope,  models  of  1904,  1905,  and  1915. 

Telescopic  musket  sight,  models  of  1908  and  1913. 
-  68.  Porro  prisms  of  all  telescopes  mentioned  above  are  fixed  in 
position  in  a  holder  and  do  not  permit  of  adjustment  as  in  the  case 
of  Brashear-Hastings  prisms.  Each  telescope  is  tested  for  adjust- 
ment of  prisms  before  it  leaves  the  manufacturer  and  no  change 
should  be  found  necessary.  Telescopes  with  Porro  prisms  are  ordi- 
narily collimated  by  moving  the  cross-wire  holder.  In  a  few  tele- 
scopes the  objective  can  be  adjusted  as  in  the  case  of  the  telescope 
for  the  Swasey  depression  position  finder,  types  AI  and  All. 

3-INCH  TELESCOPIC   SIGHT,   MODEL  OF   1904  AFTER  NO.   26. 
(See  Plate  III,  Pamphlet  No.  1955.) 

69.  To  dismount  eyepiece. — Plate  III,  Form  No.  1955,  indicates 
clearly  the  construction  and  method  of  dismoimting  the  eyepiece. 
No  attempt  should  be  made  to  remove  the  lenses  of  the  eyepiece 
from  their  cells. 

70.  To  dismount  the  prisms. — To  take  off  the  prism  holder,  unscrew 
aU  screws  and  remove  the  holder  from  the  telescope  body  by  simply 
raising  the  holder  from  the  telescope  body;  push  down  one  end  of  the 
prism  spring  to  disengage  the  recess  or  receiver  and  pull  or  turn  the 
spring  sideways.  If  this  is  done,  and  the  spring  removed,  the  prism 
is  ready  to  be  taken  out.  Care  must  be  taken  after  cleaning  the 
prism  that  it  is  mounted  in  the  same  position  as  before. 

71.  The  prism  holders  on  sights  after  No.  297  differ  somewhat 
from  those  that  preceded.  The  holder  is  separate  from  the  cover 
and  is  secured  to  the  tube  by  five  screws,  three  entered  from  the 
outside  of  the  tube  on  the  right  hand  and  two  entered  inside  the  cover 
through  a  shoulder  on  the  prism  holder.  The  cover  is  in  two  pieces, 
the  smaller  of  which  is  secured  to  the  right-hand  side  of  the  prism 
holder  by  three  screws.  The  larger  is  secured  to  the  smaller  by 
three  screws  and  to  the  prism  holder  on  the  left  side  by  two  screws ;  in 
addition,  one  screw  secures  it  to  the  rear  flange  of  the  prism-holder 
seat  and  one  to  the  front  flange.  In  dismounting,  first  remove  the 
larger  piece  of  the  cover  and  then  the  smaller,  w^hen  the  prism  holder 


may  be  taken  out.  The  parts  should  be  assembled  in  reverse  order. 
The  method  of  removing  the  prisms  from  the  holder,  cleaning,  and 
reassembling  is  the  same  as  that  described  in  preceding  paragraph. 

72.  To  dismount  the  objective. — Unscrew  the  objective  holder  and 
lay  it  on  a  clean  table  covered  with  fine  white  paper.  Then  unscrew 
the  ring  securing  the  three  lenses  (56)  in  the  holder.  Be  careful  that 
the  two  black  paper  rings  which  separate  the  lenses  are  not  lost. 
Before  taking  the  lenses  apart,  put  a  soft-pencil  arrow  (>)  across  the 
periphery  and  in  line  with  the  optical  axis  of  the  objective,  the  point 
of, the  >  toward  the  outside  surface  of  the  objective.  This  will  serve 
to  indicate  that  the  three  lenses  must  be  put  in  the  same  position  as 
before  cleaning;  with  the  indicated  arrow  lines,  the  position  of  the 
lenses  can  not  be  changed,  because  there  is  only  one  position  where 
the  lines  of  the  arrow  will  match. 

73.  To  adjust  the  telescope. — Place  the  collimating  telescope  No.  98 
with  rings  No.  99  in  the  cradle  bearing  and  sight  on  an  object.  Test 
and  adjust  collimating  telescope  if  necessary.  .  Remove  the  collimat- 
ing telescope,  and  without  disturbing  the  position  of  the  bearings 
insert  the  telescope  to  be  adjusted,  and  by  means  of  the  cross-wire 
holder  screw  collimate  it  to  agree  with  collimating  telescope.  (See 
paragraph  62.) 

74.  Make  the  vertical  wire  parallel  with  a  plumb  line.  The  holes 
through  the  focusing  sleeve  and  draw  tube  for  reaching  the  cross-wire 
ring  screws  are  slotted  for  this  purpose.  Before  this  adjustment 
make  sure  that  the  focusing  sleeve  (51)  is  screwed  tightly  into  the 
tube.  If  the  focusing  sleeve  can  be  screwed  in  too  far,  its  flange 
should  be  packed  up  with  a  thin  piece  of  metal,  paper,  or  other  suit- 
able material. 

SWASEY    DEPRESSION    POSITION    FINDER,    TYPE    All. 

(See  Plate  C  herewith  and  Plates  I  and  II,  Form  No.  1875.) 

75.  The  eyepiece  and  objective  of  this  telescope  are  the  same  as  in 
the  type  A  instrument  and  should  be  dismounted  as  described  in  para- 
graphs 29  and  30. 

76.  To  dismount  and  replace  the  prism  (Plate  C). — Take  off  screw 
(81)  and  turn  focusing  nut  (50),  holding  the  eye  end  (53)  until  the 
thread  of  the  focusmg  nut  is  disengaged  with  the  thread  of  the  eye 
end,  and  then  slide  out  the  whole  eye  end.  Remove  screw  (86)  and 
sprmg  (87)  and  the  prism  (88)  can  be  hfted  out,  cleaned,  and  replaced 
in  position.  Take  off  eyepiece  and  micrometer  box  by  imscrewing 
screws  (82),  then  unscrew  (83),  remove  the  spring  (84),  and  the 
prism  (85)  can  be  removed,  cleaned,  and  placed  in  position  as  before. 
Insert  spring  (84)  and  screw  in  screw  (83),  assemble  micrometer  box 
and  eyepiece  to  prism  holder  with  screws  (82),  put  into  telescope,  and 
see  that  screw  (81)  fits  in  the  slot  of  the  prism  holder. 

9950—17 3 


34 

77.  To  adjust  the  telescope  for  level  and  collimation  (Plates  I  and 
II,  Form  No.  1875). — Set  the  striding  level  on  top  of  the  telescope, 
turn  the  range  crank  on  range  drum,  and  bring  the  level  bubble  in  the 
center  of  the  glass  scale;  then  reverse  the  striding  level,  and  if  the 
bubble  is  not  exactly  in  the  center  of  the  divided  glass  scale,  correct 
half  the  error  with  the  adjusting  screws  of  the  striding  level,  and  the 
other  half  with  the  range  crank  (71).  Repeat  this  several  times  until 
the  level  bubble  remains  in  the  center. 

78.  Set  the  azimuth  index  at  0  and  bring  the  striding  level  bubble 
to  the  center  of  the  glass  scale  by  turning  the  range  crank,  then  revolve 
the  whole  telescope  and  cradle  180°  on  the  vertical  spindle,  so  that 
the  azimuth  index  reads  180°.  If  the  level  bubble  should  happen  to 
be  in  the  center  of  the  glass  scale,  the  axis  is  perfectly  plumb  in 
this  position ;  but  if  the  level  bubble  is  not  in  the  center  then  half  of 
this  error  must  be  corrected  on  the  leveling  screws  (47)  and  the  other 
half  by  turning  the  range  crank  (71).  Repeat  these  readings  several 
times  and  at  the  end  set  in  azimuth  every  90°  — first  0°— 180°  and 
180° -0°,  and  then  90° -270°  and  270° -90°.  If  the  level  bubble 
remains  exactly  in  the  center,  then  the  instrument  is  correctly  leveled 
and  all  that  is  necessary  is  to  open  the  door  (74)  in  front  of  the 
range-drum  cover,  loosen  a  trifle  the  three  screws  on  the  range  drum 
and  set  the  range  drum  so  that  telescope  level  on  the  drum  corre- 
sponds with  the  index  line  of  the  range  pointer  (78).  Next  point 
the  telescope  to  some  distant  object  and  find  some  point  or  target 
bisected  by  the  cross  wires.  Then  take  off  the  striding  level  (46) ,  open 
the  two  caps  (66)  on  the  telescope  trunnion,  take  the  telescope  out  of 
the  bearings  and  reverse  the  trunnion  axis  with  the  whole  telescope, 
close  the  two  trunnion  caps,  set  the  striding  level  .on  top  of  the  tele- 
scope, and  turn  the  range  crank  so  that  the  level  bubble  is  again  in 
the  center  of  the  glass  scale.  The  cross  wires  should  exactly  bisect 
the  same  target  as  before;  if  they  do  not  they  are  either  too  high  or 
too  low  or  to  the  right  or  to  the  left.  In  eiiher  case  only  half  the 
amount  of  this  error  is  to  be  corrected  by  shifting  the  objective. 
Loosen  sUghtly  the  screws  (89),  Plate  C,  and  by  using  the  screws  (90), 
Plate  C,  always  in  opposite  directions,  loosen  one  and  tighten  the 
other  either  up  or  down  or  sideways  until  the  telescope  is  adjusted 
correctly.  This  Operation  must  be  repeated  several  times  to  insure 
correct  adjustment.  Note  that  the  horizontal  wire  may  be  moved 
in  a  vertical  plane  and  that  before  coUimating  the  horizontal  wire 
should  be  moved  to  bisect  the  field  of  view. 

79.  To  adjust  the  vertical  wire,  type  All,  serial  numbers'^ after  No. 
219  only. — In  case  the  vertical  wire  is  not  parallel  to  a  plumb  line 
loosen  the  four  screws  holding  the  wire  ring  in  the  micrometer  slide 
and  rotate  the  wire  ring  in  the  micrometer  slide  until- wire  is  plumb. 
Then  set  up  screws. 


35 

LEWIS    DEPRESSION   POSITION    FINDER,  MODEL    OF    1907. 
(See  pamphlet  No.  1876,  Description  of  Lewis  D.  P.  F.,  Model  of  1907.) 

80.  To  replace  and  to  adjust  the  cross  wires  of  telescope. — Remove 
the  eyepiece  adapter  (21)  from  the  prism  case  back.  Unscrew  the 
cross-wire  adjusting  screws  (15)  and  remove  the  cell  for  spider  lines. 
Insert  the  cross  wires  (platinum  wire  0.0005  inch  diameter  or  spider 
web)  and  replace  the  cell  for  spider  Une  in  the  eyepiece  adapter, 
taking  care  that  the  cell  for  spider  lines  is  concentric  with  the  bore 
of  the  eyepiece  adapter.  Replace  the  eyepiece  adapter  and  in  case 
the  vertical  cross  wire  does  not  appear  to  bisect  the  field  of  view 
adjust  the  position  of  the  cell  for  spider  lines  by  means  of  the  two 
cross-wire  adjusting  screws  (15)  on  the  sides  of  the  eyepiece 
adapter. 

Make  the  vertical  wire  parallel  with  a  plumb  line  set  up  at  a  dis- 
tance for  which  parallax  may  be  removed  from  the  telescope.  It  will 
be  noted  that  the  holes  through  which  the  cross-wire  adjusting  screws 
(15)  pass  are  slotted  to  permit  this  adjustment.  This  operation  may 
well  be  combined  with  the  next,  the  target  described  being  made  of 
suflB.cient  length  for  making  the  vertical  Une  plumb. 

81.  Use  fixture  No.  86,  or  any  other  surface  plate,  on  pedestal  No, 
85,  and  level  with  bench  level  No.  73.  Using  collimating  telescope 
No.  98,  with  a  convenient  set  of  rings  or  guides,  lay  off  on  a  target  a 
horizontal  line  whose  image  is  coincident  with  the  horizontal  cross 
wire.  If  the  target  is  near,  make  the  necessary  allowance  for  the 
difference  in  heights  of  the  Center  of  the  coUimating  telescope  and  of 
the  objective  of  the  Lewis  depression  position  finder  and  lay  off  a 
second  line  to  represent  the  height  of  center  of  Lewis  depression 
position-finder  telescope.  Screw  the  counterweight  of  telescope  to 
be  coUimated  to  a  position  nearest  the  center  of  the  trunnion  yoke 
(53).  Clamp  the  telescope  to  the  surface  plate  so  that  the  bar  (51) 
bears  uniformly  on  it,  or  lay  the  telescope  on  the  surface  plate  with 
the  bar  in  uniform  contact  and  support  the  outer  end  of  the  telescope. 
Adjust  the  two  cross-wire  adjusting  screws  (15)  on  the  top  and 
bottom  of  the  eyepiece  adapter  (21)  so  that  the  horizontal  cross  wire 
coincides  with  the  image  of  the  horizontal  line  of  target.  Verify  the 
adjustment  of  the  vertical  wire.     Assemble  the  telescope. 

On  instruments  Nos.  154  and  higher,  remove  the  angles  piece  at- 
tached to  the  side  of  bar  (51)  before  placing  the  telescope  on  a  surface 
plate. 

82.  On  instruments  of  serial  numbers  154  and  above  the  objective 
is  mounted  in  an  adjustable  collar,  the  axis  of  which  is  adjustable 
in  respect  to  the  axis  of  the  tube  of  the  telescope.  This  adjustment 
is  to  compensate  errors  in  manufacture  and  should  not  need  be  made 
in  the  field.  If  the  parts  are  disassembled,  center  the  adjustable 
collar  in  the  tube  so  that  about  equal  movement  of  the  objective 


36 

may  be  made  in  any  direction.  Make  the  coUimation  adjustment  by 
the  cross-wire  adjusting  screws.  If  the  collimation  adjustment  can 
not  be  made  correctly  by  those  screws,  loosen  the  four  screws 
clamping  the  adjustable  collar  to  the  flange  of  the  tube  and  by 
means  of  the  radial  screws  in  the  adjustable  collar  make  the 
necessary  correction  of  the  line  of  sight.  Kepeat  the  test  and  tighten 
all  screws. 

83.  Alternate  method. — Set  up  a  transit  or  level  so  that  the  center 
of  the  telescope  of  transit  or  level  is  in  the  same  horizontal  plane  as 
the  center  of  the  telescope  of  the  Lewis  depression  position  finder 
(or  make  the  necessary  allowance  for  difference  in  height).  Before 
measuring  to  obtain  the  center  of  the  telescope  make  the  bar  (51) 
parallel  to  the  tangent  screw  rail  as  described  in  succeeding  para- 
graph. Lay  off  a  permanent  target  to  indicate  the  position  of  the 
horizontal  plane  through  the  axis  of  the  objective  of  the  position 
finder. 

Level  the  position  finder.  Set  the  range  dial  at  some  range, 
greater  than  1,500  yards  but  less  than  the  maximum  range,  for  which 
the  compensating  bar  (14)  and  the  tangent  screw  rail  (46)  are  parallel. 
(After  releasing  the  clamp  screw  (12),  no  movement  of  the  compen- 
sating screw  (11)  should  occur  during  translation  of  the  slide  block 
(42)  even  if  the  compensating  bar  and  tangent  screw  rail  are  not  par- 
allel. The  setting  of  the  bar  and  rail,  however,  guards  against 
accidental  disturbance  of  the  compensating  screw.)  Release  the 
ijlamp  screw  (12).  Adjust  the  compensating  screw  (11)  so  that 
AS  the  slide  block  (42)  is  moved  along  the  tangent  screw  rail  (46),  the 
horizontal  cross  wire  remains  ahgned  on  the  same  external  object. 
Then  adjust  the  horizontal  cross  wire  to  bisect  the  line  previously 
laid  off. 

In  case  a  permanent  target  for  telescope  level  is  laid  off,  measure 
the  distance  between  body  (8)  and  pedestal  cap  (33)  and  when  col- 
limating  the  telescope  see  that  the  distance  between  these  parts  is 
not  appreciably  changed.  In  case  the  target  is  at  least  100  feet  dis- 
tant, a  variation  of  one  thirty-second  of  an  inch  in  the  distance  be- 
tween body  and  pedestal  cap  may  be  neglected. 

84.  To  lay  off  a  target  at  the  height  of  the  axis  of  telescope  without 
the  aid  of  a  transit  coUimate  the  telescope  on  a  surface  plate  as  de- 
scribed above,  and  mount  the  telescope  in  its  yoke  and  level  the  table. 
Set  the  range  dial  at  some  range  greater  than  1,500  yards  and  less 
than  the  maximum  reading  for  which  the  compensating  bar  (14)  and 
the  tangent  screw  rail  (46)  are  parallel.  Release  the  clamp  screw 
(12).  Adjust  the  compensating  screw  (11)  so  that,  after  unclamping 
the  nut  block  (30),  as  the  sUde  block  (42)  is  moved  along  the  tangent 
screw  rail  (46),  the  horizontal  cross  wire  remains  ahgned  on  the  same 
internal  object.     Then  lay  off  a  target  whose  image  coincides  with 


37 


the  cross  wires  and  use  this  target  for  future  coUimation  of  the 
instrument. 

85.  The  telescope  may  be  collimated  approximately  by  adjusting 
the  horizontal  wire  in  the  same  manner  as  described  in  paragraph  80 
for  the  vertical  wire — that  is,  to  bisect  the  field  of  view. 

BATTERY   COMMANDER' S   TELESCOPE,    MODELS    OF    1904   AND    1905. 

(See  Plate  E,  herewith,  pamphlet  No.  1796,  and  drawings  22-17-1  to  6,  inclusive, 
for  model  of  1905,  and  drawings,  22-2-1,,  6,  7,  8,  9,  and  10  for  model  of  1904  instru- 
ment.) 

(The  symbols  given  apply  to  the  model  of  1905  instruments  only.) 

86.  For  a  description  of  the  operations  of  disassembling  and  clean- 
ing the  battery  commander's  telescope  which  are  permitted  in  the 
field,  see  pamphlet  No.  1796  (Handbook  of  Battalion  and  Regi- 
mental Equipment  of  Field  Artillery  and  of  Fire  Control  Equipment 
of  Field  Artillery  Batteries,  with  instructions  for  its  care).  A 
description  of  the  operations  of  disassembling  the  base  of  the  instru- 
ment will  be  found  in  paragraphs  174-176  below. 

87.  To  clean  the  objective  prism  (6V). — Remove  the  telescope  from 
the  mount,  take  out  the  four  objective  prism  box  cover  screws  (5P) 
from  the  front  face  of  the  objective  prism  box  cover  (5J),  remove  the 
cover  (5J),  turn  the  telescope  over,  and  gently  tap  against  the  hand 
and  withdraw  the  objective  prism  (6V).  Before  removing  the  prism 
mark  the  top,  in  order  that  it  may  be  reassembled  in  the  same 
manner  as  originally  adjusted.  The  three  polished  surfaces  of  the 
prism  should  be  carefully  cleaned.  Reassemble  parts  in  the  reversed 
order. 

The  objective  prism  base  (5G)  should  not  be  removed  from  the 
objective  prism  box  (5H). 

88.  To  remove  the  objective. — Unscrew  the  four  objective  prism  base 
screws  (5M)  on  the  circumferential  surface  of  the  objective  prism 
base  (5G)  and  draw  off  the  objective  prism  box  (5H)  and  the  ob- 
jective prism  base  (5G)  together.  Do  not  separate  the  base  from 
the  box.  Unscrew  the  objective  cell  (5E),  clean  the  objective  lens 
(6W),  and  replace.  Do  not  attempt  to  remove  the  objective  from 
its  cell. 

89.  To  clean  the  focusing  mechanism. — The  objective  prism  and  box 
and  the  objective  cell  should  be  removed.  Then  take  out  the  focus- 
ing pinion  sleeve  screw  (5DA)  and  pull  out  the  focusing  pinion  (5U) 
and  the  focusing  pinion  sleeve  (5CA).  The  draw  tube  (5B)  may  now 
be  removed.  Carefully  clean  all  parts,  put  a  little  vaseline  on  the 
focusing  rack  (5S),  and  lightly  oil  the  draw  tube  (5B)  with  clock  oil. 
Insert  the  draw  tube  with  a  downward  spiral  motion,  align  the  focus- 
ing rack,  and  assemble  the  focusing  pinion  (5U).  The  objective  cell 
holder  (5D)  is  soldered  to  the  draw  tube  and  should  not  be  removed. 


38 

90.  To  disassemhle  the  focusing  pinion  (5U). — Loosen  the  focusing 
pinion  nut  screw  (5AA),  unscrew,  gently  tap  to  allow  the  focusing 
pinion  knob  washer  (5X)  to  drop  out,  pull  off  the  focusing  pinion 
knob  (5W),  noting  that  it  is  keyed  to  the  shaft,  and  take  off  the 
focusing  pinion  sleeve  (5CA).  Clean,  lightly  oil  with  clock  oil,  and 
assemble  in  the  reversed  manner. 

91.  For  cleaning  the  Porro  lyrisms. — It  will  be  necessary  to  take 
out  the  three  prism  cover  screws  (2KA)  in  the  axis  prism  cover 
(2LA)  and  to  remove  the  cover.  Then  unscrew  the  four  prism 
holder  screws  (2FA)  and  remove  the  axis  prism  holder  (2MA). 
Loosen  the  prism  holder  spring  screw  (2GA)  and  take  out  the  upper 
(small)  prism.  The  lower  prism  may  be  taken  out  as  soon  as  the 
prism  holder  is  removed.  Carefully  mark  the  prisms  before  removal, 
in  order  to  reassemble  them  in  the  position  for  which  they  were 
originally  adjusted.  If  these  precautions  are  taken,  no  difficulty 
should  be  experienced  in  reassembling. 

92.  To  disassemhle  the  eyepiece. — ^Take  out  the  eyepiece  screw 
(5GA)  and  pull  the  eyepiece  from  the  eyepiece  adapter  (5EA).  The 
field  lens  ceU  (5HA)  and  the  eye  lens  cell  (5JA)  may  be  unscrewed 
from  the  eyepiece  tube  (5FA).  Do  not  attempt  to  remove  the  lenses 
from  their  cells. 

93.  To  remove  the  reticule  (6H). — For  cleaning,  it  will  be  necessary 
to  unscrew  the  eyepiece  adapter  (SEA)  from  the  axis  (2PA).  But 
first  mark  the  position  of  the  eyepiece  adapter  (SEA)  as  assembled 
in  the  axis  (2PA)  by  drawing  or  scratching  a  line  across  the  top 
surface  of  the  eyepiece  end  of  the  axis  and  the  end  of  the  adapter. 
Then  unscrew  the  eyepiece  adapter  (SEA),  take  out  three  of  the 
reticule  holder  screws  (6C),  hold  the  reticule  holder  (6A)  by  the 
finger,  and  remove  the  fourth  reticule  holder  screw  and  allow  the 
reticule  holder  to  drop  out  onto  the  palm  of  the  hand.  Keep  the 
reticule  holder  screws  (6C)  and  washers  (6B)  together,  and  reassemble 
them  in  the  same  hole  from  which  removed.  Also  note  the  position 
of  the  reticule  before  disassembling,  in  order  to  put  it  back  in  the 
same  position. 

In  reassembling,  place  the  reticule  holder  (6A)  in  the  eyepiece 
adapter  (SEA)  in  the  proper  position,  insert  the  reticule  holder  screws 
(6C)  in  the  same  holes  from  which  removed.  Tighten  opposite  screws 
and  adjust  the  reticule  holder  concentric  with  the  bore  of  the  adapter. 
Test  this  position  with  inside  cahpers.  Reassemble  the  eyepiece 
adapter  (SEA)  in  the  axis  (2PA),  so  that  the  marks  made  on  the 
adapter  and  the  axis  come  opposite  each  other.  Then  assemble  the 
Porro  prisms  (if  not  in  place),  the  eyepiece,  and  the  objective  (if 
not  already  in  place). 


39 

94.  Adjustment. — ^After  assembling  all  the  parts  except  the  objec- 
tive prism  and  prism  box,  the  telescope  will  now  be  adjusted.  For 
this  purpose  carefully  level  the  base  of  the  instrument  on  a  stable 
mount  or  plate.  Put  the  telescope  in  the  trunnion  bearings  so  that 
the  axis  of  the  objective  lies  in  a  horizontal  plane.  Adjust  the  reti- 
cule holder  (6A)  by  the  reticule  holder  screws  (6C)  so  that  the  vertical 
line  on  the  reticule  is  parallel  to  a  plumb  line.  In  making  this 
adjustment  do  not  disturb  the  concentricity  of  the  reticule  holder 
and  the  eyepiece  adapter. 

95.  To  more  perfectly  coUimate  the  telescope,  set  the  azimuth 
scale  at  0  and  accurately  align  the  vertical  line  of  reticide  on  a  plumb 
line.  Keverse  the  base  180°  so  that  the  azimuth  scale  reads  32. 
Take  out  the  telescope  from  its  bearing,  turn  it  around,  and  replace  it 
in  the  trunnion  bearing.  Correct  half  the  error  of  the  vertical  line  of 
reticule  from  the  plumb  line  by  readjusting  the  reticule  holder, 
taking  care  to  keep  the  vertical  line  parallel  to  the  plumb  line.  Cor- 
rect the  remainder  of  the  error  by  rotating  the  platen  (4R)  by  the 
slow  motion  screw.  Repeat  until  the  adjustment  of  the  reticule  is 
made  satisfactory. 

96.  Then  assemble  the  telescope  in  its  normal  position,  ahgn  the 
vertical  line  of  reticule  on  a  plumb  line,  and  rotate  the  telescope  on 
its  trunnions  until  the  axis  of  the  telescope  tube  is  vertical.  Carefully 
maintain  the  position  of  the  telescope  for  direction.  Assemble  the 
objective  prism  box  (5H)  with  prism  mounted  therein,  and  tighten 
the  four  objective  prism  base  screws  (5M)  for  the  position  of  the 
prism  box  in  which  the  vertical  wire  is  aligned  on  the  plumb  line. 
Note  that  the  prism  box  can  be  rotated  slightly  to  secure  this  ad- 
justment. 

97.  Lay  off  on  a  target  a  horizontal  line  in  the  same  horizontal 
plane  as  the  axis  of  the  objective  prism.  Release  the  platen,  so  that 
it  can  revolve  freely.  Set  the  telescope  by  turning  the  elevation 
micrometer  head  (4WA)  so  that  the  telescope  will  rotate  on  a  fixed 
vertical  axis.  Change  the  adjustment  of  the  reticule,  if  necessary,  to 
bring  the  horizontal  line  of  reticule  onto  the  horizontal  hne  of  target. 
Repeat  to  test  adjustment.  Set  the  elevation  dial  (4HA)  and  the 
elevation  scale  (2S)  to  read  0  for  this  position  of  telescope.  In  case 
the  horizontal  line  of  reticide  can  not  be  ahgned  on  the  target  in  this 
manner,  it  will  be  necessary  to  change  shghtly  the  elevation  of  the 
telescope  by  turning  the  elevation  micrometer  head. 

98.  Ordinarily  the  reticule  of  the  telescope  may  be  adjusted  satis- 
factorily by  carrying  out  the  instructions  of  paragraphs  95  and  97 
above.  The  elevation  scale  and  the  elevation  dial  should  then  be 
set  to  read  0  when  the  horizontal  line  of  the  reticule  is  aligned  on  a 
line  in  the  same  horizontal  plane  as  the  axis  of  the  objective  prism. 


40 

BATTERY   COMMANDER' S   TELESCOPE,  MODEL   OF   1915. 
(See  Plate  J  herewith,  pamphlet  No.  1796,  and  drawings  22-39-1  to  13,  inclusive.) 

99.  To  clean  the  objective  prism. — Take  out  the  prism  shield  cell 
screws,  unscrew  the  prism  shield  cell,  release  lock  nuts,  and  with- 
draw objective  prism.  The  three  polished  surfaces  of  the  prism 
should  be  carefully  cleaned.  Reassemble  parts  in  the  reversed 
order.     The  prism  adjusting  ring  should  not  be  disturbed. 

100.  To  remove  the  objective. — ^Take  out  the  telescope  tube  screw 
(upper),  remove  the  objective  prism  holder,  take  out  objective  cell 
retaining  screws,  and  withdraw  the  objective  in  its  cell.  Do  not 
attempt  to  remove  the  objective  from  its  cell.  Clean  the  objective 
and  replace. 

101.  To  remove  the  eye  lens. — ^Take  out  hood  retaining  screw,  re- 
move the  hood,  take  off  the  focusing  nut  sleeve,  take  out  the  three 
focusing  nut  retaining  screws,  then  remove  the  focusing  nut;  the 
eye  lens  and  its  cell  may  now  be  unscrewed.  Do  not  remove  the 
eye  lens  from  its  cell. 

102.  To  disassemble  the  eyepiece. — Take  out  reticule  adjusting  ring 
screw,  remove  the  reticule  adjusting  ring,  take  out  eyepiece  tube 
retaining  screw,  and  unscrew  the  eyepiece.  The  reticule  may  now 
be  removed  for  cleaning     Reassemble  the  parts  in  the  reversed  order. 

103.  To  disassemble  the  elevation  worm  mechanism,. — Take  out  the 
two  eye  distance  scale  screws,  remove  the  eye  distance  scale,  un- 
screw end  bearing  lock  nut,  and  remove  the  elevation  worm  end 
bearing  and  elevation  worm  washer.  By  next  driving  out  steel 
pin  the  elevation  worm  knob  can  be  removed  and  the  elevation 
worm  withdrawn. 

OBSERVATION   TELESCOPE,  FIELD,  MODEL   OF   1908. 
(See  Pamphlet  No.  1796.) 

104.  The  lenses  forming  the  objective  of  this  telescope  are  cemented 
and  the  objective  should  not  be  removed  from  its  cell  for  cleaning. 

105.  To  clean  the  prisms. — ^Remove  the  cover;  but  unless  after 
cleaning  the  exposed  surfaces  dirt  or  moisture  is  seen  on  the  unex- 
posed surfaces,  the  holder  shoidd  not  be  removed  from  the  cover  nor 
the  prisms  from  the  holder.  If  it  is  found  necessary  to  clean  the  un- 
exposed surfaces,  remove  the  screws  which  hold  the  holder  to  the 
cover  and  then  pull  the  holder  and  cover  apart.  Then  remove  a 
prism-retaining  spring  and  take  out  one  prism.  Only  one  prism 
need  be  removed  from  the  holder.  The  prism  should  be  marked 
before  disassembling,  in  order  that  it  may  be  replaced  in  exactly  the 
same  manner.    Do  not  reverse  the  prism,  as  it  has  been  adjusted  by 


41 

the  manufacturer  and  tested  for  the  adjustment  in  which  it  is  issued 
to  the  service.  In  reassembling,  note  that  the  prism  holder  is  located 
on  the  cover  by  two  dowel  pins. 

TELESCOPIC   MUSKET   SIGHT,  MODEL   OF    1908. 
(See  Pamphlet  No.  1957.) 

106.  As  stated  in  pamphlet  No.  1957,  the  body  of  this  telescope  and 
its  objective  must  remain  intact  and  the  prism  holder  should  never 
be  opened  except  by  a  competent  person.  In  case  moisture  collects 
on  the  interior  optical  surfaces,  it  may  be  evaporated  by  imparting 
a  gentle  warmth  to  the  telescope. 

107.  Removal  of  prisms. — The  prism  holder  is  tightly  fitted  to  the 
body  to  prevent  the  access  of  dust,  moisture,  etc.,  into  the  interior 
and  is  held  to  the  body  by  five  body  screws.  After  removal  of  these 
screws  the  prism  holder  may  be  withdrawn  from  the  body.  Care- 
fully clean  the  polished  surfaces  of  the  prisms  without  removing  them 
from  their  holder.  The  prisms  should  be  withdrawTi  from  their 
holder  for  repairs  or  for  adjustment  of  the  telescope  by  an  instrument 
maker  only.  Replace  the  holder  so  that  the  prisms  are  in  the  same 
relation  to  the  lenses  as  before  removed. 

108.  Removal  of  lenses. — The  objective  and  cell  may  be  removed  for 
cleaning  by  unscrewing,  the  cell  being  held  only  by  the  screw  thread 
on  its  periphery.  The  reticule  holder  is  adjusted  by  special  tests  by 
the  manufacturer  and  should  not  be  disturbed.  The  objective,  reti- 
cule, and  eyepiece  are  crimped  in  their  ceUs  and  should  never  be  re- 
moved. 

109.  If  the  objective  cell  is  removed,  care  should  be  taken  to  screw 
it  in  tightly  when  assembling,  as  in  this  sight  the  location  of  the 
objective  in  respect  to  the  reticule  is  made  for  a  medium  range  and 
should  not  be  varied.  Aside  from  the  adjustment  permitted  for 
focusing  the  eyepiece,  the  construction  of  the  telescope  admits  of  no 
adjustment  except  by  an  experienced  instrument  maker.  In  case 
parallax  can  not  be  removed  for  medium  ranges  the  sight  should  be 
shipped  to  an  arsenal  for  overhauling. 

TELESCOPIC   MUSKET   SIGHT,  MODEL   OF    1913. 
(See  Pamphlet  No.  1957.) 

110.  This  instrument  is  identical  with  the  model  of  1908,  except 
that  the  objective  is  mounted  in  the  objective  cell  and  held  in  place 
by  the  objective  retaining  nut. 


42 

PANORAMIC   SIGHT,    MODEL   OF    1904. 
(See  Plate  D  herewith,  Pamphlet  No.  1659,  and  Drawings  15-2AII-1  to  6,  inclusive.) 

111.  Sealing  of  sights. — In  all  panoramic  sights  in  which  the  shutter 
window  (5K)  is  inserted  in  the  eyepiece  elbow  (6E)  and  in  those 
sights  having  the  shutter  window  burnished  in  the  shutter,  which 
have  been  issued  from  Frankford  Arsenal  later  than  May  1,  1912,  all 
exposed  optical  elements  and  machined  joints  leading  to  the  interior 
chambers  of  the  sight  which  contain  optical  elements,  are  sealed  with 
litharge  cement.  No  parts  of  such  sights  except  the  worm  box 
mechanism  and  the  movable  index  cover  will  be  removed  except  at 
an  arsenal  or  other  establishment  equipped  for  repairing  panoramic 
sights.  The  parts  of  the  sight  which  may  be  removed  in  the  field 
are  specified  by  pamphlet  No.  1659  (Handbook  of  the  3-inch  Field 
Artillery  Materiel). 

112.  The  optical  parts  of  the  panoramic  sight  should  be  removed 
only  in  case  of  necessity.  This  sight  is  a  delicate  instrument  and  is 
difficult  to  adjust  accurately.  In  case  moisture  condenses  on  the 
optical  parts  of  unsealed  sights  it  may  be  evaporated  by  allowing  the 
sight  to  stand  in  a  warm,  dry  room.  No  part  of  the  sight  should  be 
disassembled  for  which  specific  directions  are  not  given  below,  and 
then  only  after  careful  study  of  the  following  paragraphs  and  the 
pamphlet  referred  to  above.  In  case  the  method  of  reassembhng  is 
not  given  it  should  be  done  in  the  reversed  order  to  which  the  parts 
are  disassembled. 

113.  To  clean  the  rotating  head  window  (5D). — Unscrew  the  window 
ceU  in  rotating  head  (2P).     Do  not  remove  the  window  from  the  cell. 

114.  To  disassemble  the  eyepiece. — ^Remove  the  set  screw  from  the 
underside  of  the  eyepiece  elbow  (6E)  and  unscrew  the  field  lens  cell 
(6N).  For  cleaning  the  lenses,  remove  the  set  screw  (3Z)  on  underside 
of  field  lens  cell  (6N)  and  unscrew  the  eye  lens  cell  (6L).  The  field 
lens  (5M)  is  held  in  place  by  the  field  lens  retaining  spring  (6R) 
both  of  which  may  drop  out  as  soon  as  the  eye  lens  cell  is  disas- 
sembled. In  reassembhng  note  that  the  field  lens  should  be  assem- 
bled with  its  flat  surface  toward  the  reticule  (5K). 

115.  Disassembling  of  azimuth  circle  mechanism. — If  it  is  necessary 
to  disassemble  the  azimuth  circle  mechanism,  throw  out  the  worm- 
box  eccentric  lever  (4A),  disengaging  the  worm  (4 J)  from  the  worm 
gear  on  the  azimuth  circle  (2E).  Insert  a  pin  in  the  radial  hole  in  the 
spring-box  pin  for  worm  box  (4B).  Throw  the  eccentric  lever  (4A) 
back  and  engage  the  worm  in  the  azimuth  circle  (2E).  Push  the 
spring  box  (411)  toward  the  worm  knob  (4N)  about  J  inch  and  then 
pull  the  spring  box  straight  out.  Take  out  the  stud  (3M)  from  worm- 
box  eccentric  lever  (4A)  and  remove  the  worm-box  eccentric  lever 
(4A).   '  Pull  out  the  dowel  for  worm-box  pin  (4G)  with  a  pair  of 


43  • 

pliers  and  drive  out  the  worm-box  pin   (4F).     Then  pull  out  the 
worm  box  (4B)  and  the  worm  (4J)  complete. 

116.  To  clean  the  worm  (4J)  remove  the  worm  knob  (4N)  and 
draw  the  worm  (4J)  from  the  worm  box  (4B).  Do  not  remove  the 
worm  index  (4E)  from  the  worm  (4J),  in  order  not  to  change  the 
adjustment  of  the  azimuth  mechanism. 

117.  To  disassemble  the  azimuth  circle,  etc. — Remove  the  five  radial 
screws  from  the  hood  for  azimuth  circle  (2F)  and  unscrew  it  from 
the  azimuth-circle  support  (5C).  Remove  the  window  cell  in  totat- 
ing  head  (2N)  if  it  is  not  already  disassembled.  Then  lift  the  hood 
for  azimuth  circle  (2F)  from  the  sight. 

118.  Before  removing  the  azimuth  circle  (2E),  the  rotating  head 
(2N),  etc.,  turn  those  parts  until  the  0  on  the  azimuth  circle  (2E)  is 
opposite  the  center  of  the  supporting  lug  on  the  eyepiece  end  of  the 
shank.  Then  pull  the  azimuth  circle  (2E)  and  the  rotating  head  (2N) 
straight  off  without  rotating  the  gears  by  the  least  amount.  Mark 
the  tooth  on  the  large  pinion  (2LA)  which  is  opposite  the  nearest 
corner  of  the  rotating  prism  (5B) .  Then  make  a  mark  on  the  rotating 
prism  holder  (4Q)  directly  opposite  the  marked  tooth  of  the  pinion. 
Drive  out  the  pinion  shaft  (2MA)  from  the  underside  of  the  azimuth- 
circle  support  (5C).  Move  the  pinions  opposite  the  opening  in  the 
azimuth-circle  support  (5C)  and  withdraw  by  inverting  the  sight. 
Grasp  the  rotating  prism  holder  (4Q)  and  withdraw  the  rotating 
prism  (5B)  and  the  rotating  prism  holder  (4Q)  and  the  supporting 
sleeve  for  rotating  prism  (5A)  from  their  seat  in  the  shank  (5L). 

119.  Do  not  remove  the  covers  for  rotating  head  (2M)  and  do  not 
disassemble  the  rotating  head  (2N)  and  the  azimuth  circle  (2E)  from 
the  azimuth-circle  hub  and  gear  (2D) ;  also  do  not  remove  the  rotat- 
ing prism  (5B)  from  the  rotating  prism  holder  (4Q)  nor  the  rotating 
prism  holder  (4Q)  from  the  supporting  sleeve  for  rotating  prism  (5A). 
Also  do  not  disturb  the  adjustment  of  the  lower  reflecting  prism  (5J). 
These  parts  may  be  disassembled  only  by  an  expert  instrument 
maker  with  proper  facilities  for  readjusting,  etc. 

120.  Cleaning  and  oiling. — Carefully  clean  all  gears  and  exposed 
surfaces  of  metal  parts.  Benzine  may  be  used  in  cleaning  the  worm 
and  gear  teeth.  Apply  it  with  a  toothbrush  or  similar  brush.  After 
thoroughly  cleaning,  put  a  little  vaseline  on  the  worm  and  gear  teeth 
and  a  little  clock  oil  on  the  inside  circiunferential  and  lower  surfaces 
of  the  azimuth  circle  (2E)  and  the' outside  surface  of  the  supporting 
sleeve  for  rotating  prism  (5A).  Two  drops  of  clock  oil  on  each  of 
the  parts  is  sufficient  for  proper  lubrication.  Never  use  emery  cloth, 
crocus  cloth,  or  any  abrasive  on  any  part  of  the  panoramic  sight. 
Be  careful  not  to  allow  any  oil  to  drop  on  the  glass  surfaces.  Leave 
no  free  oil  to  run  down  onto  glass  surfaces  after  reassembling. 


44 

121.  Clean  the  exposed  surfaces  of  the  rotating  head  prism  (5E) 
and  the  rotating  prism  (5B).  Use  a  soft  cloth  free  from  lint  on  a 
stick  to  reach  such  surfaces  as  can  not  be  otherwise  reached  for 
cleaning.  After  carefully  wiping  the  optical  surfaces,  brush  them 
with  a  camel  hair  brush.  Do  not  in  any  manner  change  the  adjust- 
ment of  these  prisms. 

122.  In  reassemhling,  insert  the  rotating  prism  holder  (4Q)  and  the 
parts  assembled  thereto  and  bring  the  mark  made  on  the  rotating 
prism  holder  (4Q)  opposite  the  pinion  shaft  (2MA)  seat.  Insert  the 
pinions  for  rotating  prism  (2LA)  and  rotating  head  (2N)  through 
the  opening  in  the  azimuth-circle  support  (5C)  and  engage  the  teeth 
of  pinion  and  gear  so  that  the  mark  made  on  a  tooth  of  the  pinion 
comes  opposite  the  mark  made  on  the  holder.  Insert  the  pinion 
shaft  (2MA).  Place  the  azimuth  circle  (2E)  and  the  attached  parts 
over  the  azimuth-circle  support  (5C)  without  engaging  any  teeth,  and 
rotate  the  azimuth  circle  (2E)  so  that  the  0  of  scale  comes  opposite 
the  supporting  lug  on  the  front  face  of  the  shank  (5L).  Then  drop 
the  azimuth  circle  (2E)  in  place  and  reassemble  other  parts. 

123.  To  remove  the  objective  lens  (5H). — Special  tools  not  furnished 
with  sights  are  required.  For  this  purpose  take  out  the  four  radial 
screws  in  the  lower  part  of  the  shank  (5L).  First  note  whether 
opposing  marks  are  on  the  upper  surface  of  the  eyepiece  elbow  (6E) 
and  the  lower  surface  of  the  shank.  If  not,  scratch  a  light  mark  on 
these  two  surfaces,  in  order  that  the  parts  may  be  reassembled  in 
exactly  the  same  position  as  originally  adjusted.  Then  put  the  eye- 
piece elbow  (6E)  in  a  vise.  Use  spanner  wrench  and  block  No.  34 
(furnished  with  tools  and  fixtures  for  optical  repair  work)  and  unscrew 
the  elbow  from  the  shank  (5L).  Remove  the  set  screw  in  the  upper 
end  of  the  eyepiece  elbow  (6E).  Use  spanner  wrench  No.  32  and 
unscrew  the  objective  lens  cell  (6A).  Do  not  remove  the  lens  from 
its  cell. 

124.  To  disassemble  the  reticule  (5K). — Remove  the  two  screws  in 
the  adjusting  block  for  reticule  cell  (6H)  and  gently  shake  out  the 
reticule  cell  (6G).  The  reticule  should  not  be  disturbed  in  its  cell. 
In  cleaning  the  reticule  (6G),  use  cloth  as  free  as  possible  from  lint. 
After  cleaning  it,  examine  its  surface  with  a  magnifier  (the  eyepiece 
may  be  used  for  this  purpose),  and  if  not  perfectly  clean  reclean  it. 
Use  a  camel  hair  brush  for  wiping  off  dust  and  lint.  This  special 
precaution  is  necessary,  as  the  reticule  is  in  the  focal  plane  of  the 
eyepiece  and  any  dust  thereon  wiU  be  magnified. 

125.  Lower  reflecting  prism. — With  the  objective  lens  cell  (6 A)  and 
the  reticule  cell  (6H)  removed,  the  lower  reflecting  prism  (5J)  may 
be  cleaned.  For  this  purpose  remove  also  the  eyepiece  elbow  covers 
(6B)  and  clean  the  back  surfaces  as  well  as  the  faces  of  this  prism. 
In  this  connection  note  paragraphs  119  and  121  above. 


45 

126.  Adjustment  of  reticule. — When  reassembling  the  reticule  cell 
(6G),  insert  the  adjustable  block  for  reticule  cell  (6H),  but  do  not 
tighten  the  screws.  After  all  other  parts  of  the  sight  are  assembled 
adjust  the  reticule  ceU  (6G)  so  that  the  vertical  line  is  parallel  to  a 
plumb  line.  The  reticule  ceU  (6G)  and  the  adjustable  block  for 
reticule  cell  (6H)  may  be  slightly  rotated  for  this  purpose.  Also 
adjust  the  reticule  cell  (6G)  by  translating  it  longitudinally  until  it 
is  in  the  focal  plane  of  the  eyepiece  and  there  is  no  parallax  when 
observing  objects  at  least  1  mile  distant.  To  secure  this  adjustment, 
the  objective  lens  cell  (6 A)  must  have  been  replaced  in  exactly  the 
same  position  as  before  disassembling.  In  order  that  the  field  may 
be  vertical,  the  eyepiece  elbow  (6E)  must  be  screwed  up  so  that  the 
marks  on  it  and  the  shank  (5L)  come  opposite  each  other  and  the 
eyepiece  elbow  (6E)  is  entered  by  the  same  number  of  threads. 
Great  care  must  be  taken  in  reassembling  the  sight. 

127.  If  the  field  is  not  vertical,  either  the  rotating  prism  (5B)  has 
been  wrongly  assembled  or  the  eyepiece  elbow  (6E)  has  not  been  prop- 
erly screwed  up.  If  parallax  can  not  be  removed,  either  the  objective 
lens  cell  (6A)  or  the  field  lens  cell  (6N)  or  the  reticule  cell  (6G)  has 
been  incorrectly  assembled.  For  adjusting  the  reticule  cell  (6G)  the 
panoramic  sight  may  be  mounted  in  its  seat  on  the  rear  sight  or  it 
may  be  mounted  in  vertical  fixture  No.  89  (furnished  with  tools  and 
fixtures  for  optical  repair  work).  Fixture  No.  89  is  used  on  round 
surface  plate  No.  88,  which  should  be  centered  and  leveled  on  pedestal 
No.  85. 

128.  Adjustment  of  azimuth  circle. — Ordinarily  the  azimuth  circle 
(2E)  will  be  set  with  the  panoramic  sight  in  its  seat  on  the  rear 
sight  as  described  in  pamphlet  No.  1659.  It  will  be  corrected 
for  errors  in  the  rear  sight  or  its  support.  It  may,  however,  be  ad- 
justed independently  of  the  rear  sight  as  follows:  Mount  hori- 
zontal fixture  No.  86  in  pedestal  No.  85  and  carefuUy  level.  Screw 
guide  for  coUimating  telescope  No.  90  in  horizontal  fixture  No.  86 
and  align  collimating  telescope  No.  90  on  a  plumb  line.  Clamp  the 
fixture  in  place,  remove  the  collimating  telescope  and  guides,  and 
secure  the  panoramic  sight  shank  clamp  to  the  horizontal  fix:ture. 
Set  panoramic  sight  at  the  azimuth  of  48  and  insert  it  in  the  seat 
prepared  for  it  on  the  horizontal  fixture,  turn  the  worm  knob  (4N), 
and  align  the  line  on  the  reticule  with  a  plumb  line  without  changing 
the  setting  of  the  fixture.  Then  adjust  the  azimuth  circle  to  read 
48  when  the  line  on  the  reticule  (5K)  coincides  with  a  plumb  line. 
For  adjusting  the  azimuth  circle,  note  that  the  movable  index  cover 
(2UA)  may  be  moved  and  that  the  worm  index  (4E)  on  the  worm 
(4 J)  may  be  adjusted. 

129.  The  azimuth  circle  of  a  panoramic  sight  must  be  adjusted 
for  a  particular  gun  and  for  a  particular  rear  sight.     The  adjustment 


46 

of  the  worm  index  (4E),  the  movable  index  cover  (2UA),  and  the 
worm  (4J),  as  made  by  the  manufacturer  of  the  panoramic  sight, 
will  probably  not  be  found  correct  for  a  particular  gun.  It  is  intended 
that  the  final  adjustment  of  the  azimuth  circle  (2E)  of  a  panoramic 
sight  be  made  by  the  battery  commander  by  making  the  line  of  sight 
of  the  panoramic  sight  parallel  to  the  axis  of  the  bore  of  the  gun 
and  setting  the  scales  accordingly. 

130.*  Special  notes  on  adjusting  panoramic  sights. — The  larger  rec~ 
tangular  surface  of  the  rotating  prism  is  polished  and  is  known  as  the 
''base." 

To  adjust  the  rotating  prism  in  its  holder,  put  shank  with  elbow 
and  eyepiece  assembled  in  horizontal  fixture  No.  86  with  eyepiece  up. 
Direct  telescope  at  a  plumb  hne.  Insert  the  rotating  prism  wrapped 
with  paper  as  described  below  into  the  holder  and  the  holder  into  the 
supporting  sleeve  for  rotating  prism  and  assemble  them  in  the  shank 
without  the  gearing.  Turn  the  prism  so  that  the  end  surfaces  lie  in 
vertical  planes  and  a  plumb  line  appears  parallel  to  the  vertical  line 
of  the  reticule.  Move  the  fixture  if  necessary  to  make  the  image  of 
the  plumb  line  coincide  with  the  vertical  line  of  reticule.  Then  turn 
the  rotating  prism  180°  until  plumb  line  again  appears  parallel  to  the 
vertical  line  of  the  reticule.  Correct  half  the  error  of  deviation  of  the 
vertical"  line  on  the  reticule  from  a  plumb  line  by  slightly  fihng  off  and 
slightly  bending  over  the  supporting  walls  of  the  upper  and  lower 
ends  of  the  prism  holders.  Note  that  if  the  upper  surface  is  bent 
toward  the  axis  of  the  holder  the  lower  surface  on  the  same  side  of 
holder  should  be  filed  by  an  equal  amount,  as  the  prism  should  be 
rotated  on  one  of  its  shorter  axes.  The  filing  or  bending  of  holder 
should  be  only  on  the  surface  prepared  for  the  base  of  the  prism  and 
the  opposite  surface.  Do  not  touch  the  other  two  surfaces  of  the 
prism  holder.  The  amount  of  metal  to  be  taken  off  will  be  only  a  few 
thousandths  of  an  inch.  Then  rotate  the  fixture  to  again  bring  the 
vertical  line  of  the  reticule  on  the  plumb  line  and  repeat  the  test. 
Before  assembling  the  prism  in  its  holder  for  test  or  final  adjustment 
partially  wrap  the  prism  with  a  sheet  of  dull  black  paper  0.005  inch 
thick  of  the  length  of  the  bearing  surface  of  the  holder.  For  this 
purpose  turn  back  one  edge  of  the  paper  ^  inch  against  the  polished 
surface  of  the  base,  then  wrap  the  paper  over  the  three  unpolished 
surfaces  and  turn  it  over  the  other  edge  of  the  base  and  cut  so  that 
it  extends  -^  inch  beyond  the  edge  of  the  base.  After  final  adjust- 
ment of  rotating  prism  insert  the  set  screw  in  prism  holder.  Note  that 
the  set  screw  should  not  bottom  in  the  notch  in  the  rotating  prism. 

131.*  In  adjusting  the  prisms  of  this  sight  the  following  intruc- 
tions  should  be  followed :  It  is  assumed  that  the  lenses  and  mountings, 
the  rotatingiprism,  the  pinions  and  pinion  shaft,  the  azimuth  circle,. 

*  See  paragraph  11. 


47 

and  the  rotating  head  are  assembled.  Use  vertical  fixture  No.  89  on 
pedestal  No.  85,  with  round  surface  plate  No.  88.  Carefully  level 
and  place  the  panoramic  sight  in  the  socket  of  vertical  fixture  No.  89. 
Now  look  through  the  eyepiece.  If  the  field  of  view  seems  to  incline 
either  to  the  right  or  left,  it  will  be  necessary  to  remove  the  rotating 
head  and  the  azimuth  circle  and  change  the  relation  of  the  prism  to 
the  larger  gears.  This  change  is  made  by  removing  the  pinion  shaft 
and  turning  the  pinion  until  those  teeth  are  in  mesh,  which  bring 
the  field  of  view  into  a  vertical  position.  This  operation  usually 
requires  much  care  and  time.  If  it  be  found  after  long  trial  that  one 
position  of  the  teeth  gives  better  results  than  any  other  position,  but 
that  the  results  are  not  yet  satisfactory  as  to  verticality  of  the  field,, 
it  wiU  then  be  necessary,  having  determined  this  best  position  of  the 
teeth,  to  make  the  ultimate  adjustment  for  verticality  of  the  field 
on  the  rotating  prism  and  rotating  prism  holder.  To  do  this,  unscrew 
the  rotating  prism  holder  screw,  securing  the  rotating  prism  holder 
to  the  supporting  sleeve  for  rotating  prism.  The  rotating  prism 
holder  with  rotating  prism  may  then  be  revolved  in  the  supporting 
sleeve  by  hand  until  the  field  assumes  the  correct  vertical  position. 
Having  obtained  the  position,  clamp  the  rotating  prism  holder  and 
the  supporting  sleeve  carefully  together  and  driU  and  tap  a  new  hole 
for  the  set  screw.  The  field  adjustment  should  now  be  satisfactory. 
The  pinion  and  gear  teeth  which  are  in  mesh  to  give  verticality  of 
field  should  be  spot  marked  for  future  adjustment.  These  marks, 
are  readily  recognized  by  any  machinist  or  instrument  maker  and 
no  difficulty  should  be  experienced  in  at  once  bringing  the  field  into 
proper  adjustment.  Also  note  that  the  portion  of  the  above  descrip- 
tion relating  to  the  removal  of  the  set  screw  securing  rotating  prism 
holder  and  supporting  sleeve  together  is  intended  to  be  applied  only  in 
extreme  cases,  when  from  violent  accident  great  injury  to  the  parts 
of  the  panoramic  sight  has  been  produced.  In  such  cases  the  adjust- 
ment must,  of  course,  proceed  on  the  same  lines  as  if  the  parts  had 
never  been  assembled  together.  In  the  general  case,  however,  na 
need  will  be  found  for  removing  the  set  screw  and  redriUing.  It 
may  occasionally  be  necessary  to  loosen  the  set  screw  slightly,  and 
then  push,  by  the  merest  hair  the  rotating  prism  holder  in  one  direc- 
tion or  the  other,  again  tightening  the  screw.  But  caution  is  enjoined 
for  any  such  operation. 

132.*  Replace  rotating  head,  azimuth  circle,  etc.  The  sight  still 
mounted  in  the  vertical  fixture  is  then  directed  toward  a  target  at 
the  same  height  as  the  center  of  the  window  ceU.  Such  a  target 
should  be  laid  out  carefully,  using  an  accurate  transit  or  Y  leveL 
Now  look  through  the  eyepiece  of  the  panoramic  sight.  The  hori- 
zontal line  of  the  reticule  from  end  to  end  should  appear  at  the  same 

♦See  paragraph  11. 


4M 

height  as  the  fixed  target  selected.  If  the  cross  line  appears  above 
or  below  the  target,  correction  should  be  made  on  the  lower  reflecting 
prism  and  not  on  the  reticule.  The  necessary  correction  shoidd  be 
made  by  fihng  carefnUy  the  brass  bearings  of  the  seat  for  the  lower 
reflecting  prism  in  such  a  way  as  to  make  the  prism  lean  forward  or 
backward,  as  the  case  may  be,  an  amount  sufl3.cient  to  correct  for 
the  full  error.  This  operation  is  extremely  dehcate,  and  the  fihng  or 
scraping  should  be  proceeded  with  most  carefully.  The  bearing 
surfaces  of  the  prism  seat  must  be  cut  away  to  produce  a  change  in 
the  position  of  the  prism  from  front  to  rear,  or  the  reverse  only, 
but  lateral  tilting  produced  by  leaving  the  seat  higher  on  one  side 
than  the  other  must  be  avoided. 

PANORAMIC    SIGHT,    MODEL   OF   1915. 
(See  Plate  K  herewith,  Pamphlet  No.  1659,  and  Drawings  15-15G-1  to  10,  inclusive.) 

133.  The  optical  parts  of  the  panoramic  sight  should  be  removed 
only  in  case  of  necessity  and  then  by  order  of  an  officer  of  the  Ord- 
nance Department.  All  the  joints  are  sealed  when  they  leave  the 
manufacturer  and  any  disassembhng  wiU  break  this  seal  and  allow 
dust  and  moisture  to  enter.  In  case  moisture  condenses  on  the 
optical  parts  of  unsealed  sights,  it  may  be  evaporated  by  allowing 
the  sight  to  stand  in  a  warm,  dry  room.  This  sight  is  a  dehcate 
instrument  and  is  difficult  to  adjust  accurately.  Reassembling 
should  be  done  in  the  reversed  order  to  which  the  parts  were  disas- 
sembled. 

134.  To  disdssemhle  the  eyepiece. — Take  out  the  eye  lens  ceU  retain- 
ing screw,  remove  the  eye  lens  cell  and  reticule  cell.  To  clear  the 
lenses,  take  out  the  reticule  cell  rietaining  screw,  unscrew  reticule 
cell  in  which  the  reticule  is  permanently  fastened,  take  out  field  lens 
retaining  ring  screw  and  unscrew  the  field  lens  retaining  ring  which 
permits  the  field  lens  and  eye  lens  to  be  removed.  In  reassembhng 
note  that  the  eye  lens  and  field  lens  be  assembled  with  their  curved 
surfaces  toward  each  other. 

135.  To  disassemble  the  rotating  head  mechanism  with  the  elevation 
device  from  the  instrument. — Remove  the  four  azimuth  scale  retain- 
ing ring  screws  and  unscrew  the  rotating  head  from  the  upper  end 
of  the  azimuth  worm  wheel.  The  azimuth  scale  with  azimuth  scale 
retaining  ring  can  now  be  removed.  To  disassemble  the  elevation 
device,  loosen  the  locking  screw,  remove  the  elevation  worm  microme- 
ter head,  loosen  the  elevation  worm  retaining  nut  screw,  and  then 
remove  the  elevation  worm  retaining  nut.  The  elevation  worm  can 
now  be  removed  by  turning.  To  unscrew  the  rotating  head  cover, 
remove  the  rotating  head  cover  screw.  Remove  the  prism  holder 
cover  screw  and  unscrew  the  prism  holder  screw.  Remove  the  two 
elevation  index  retaining  screws  and  then  elevation  index  can  be 


49 

lifted  from  the  elevation  index  support.  Remove  the  support 
retaining  ring  screw  and  unscrew  the  support  retaining  ring.  Remove 
the  elevation  index  support  screw  and  unscrew  the  elevation  index 
support.  Drive  out  the  segment  lock  pin  and  the  elevation  segment 
will  drop  from  its  seat  to  the  interior  of  the  head.  Unscrew  the 
rotating  head  prism  holder  stop  screw  and  then  withdraw  the  rotating 
head  prism  holder.  The  elevation  segment  can  now  be  removed  by 
using  the  fingers.  To  remove  the  elevation  worm  bushing  loosen  the 
bushing  clamp  plug  screw  which  releases  the  elevation  worm  bushing 
clamp  plug.  Remove  the  rotating  head  spring  which  releases  the 
prism  support  back,  and  then  remove  the  rotating  head  prism.  The 
prism  shield  can  be  removed  by  unscrewing  the  two  prism  shield 
retaining  piece  screws  and  removing  the  prism  shield  retaining  piece. 

136.  To  disassemble  the  azimuth  mechanism. — Loosen  the  locking 
screw,  remove  the  azimuth  micrometer,  drive  out  the  taper  pin  from 
the  worm  knob,  unscrew  the  worm  knob  and  remove  the  lever  spring, 
take  out  azimuth  worm  lever  screw  and  remove  the  azimuth  worm 
lever.  The  azimuth  worm  may  now  be  withdrawn  by  turning  and 
the  azimuth  worm  bushing  and  bushing  spring  can  now  be  removed. 
Remove  the  three  deflection  worm  wheel  and  support  ring  screws, 
then  unscrew  and  dismount  the  azimuth  worm  wheel  cover.  Re- 
move the  azimuth  worm  wheel  support  spring  and  azimuth  worm 
wheel.  Disassemble  the  azimuth  worm  wheel  support  with  interior 
mechanism.  Drive  out  the  pinion  shaft  which  will  allow  the  rotating 
head  pinion  to  slide  into  the  slot  in  the  azimuth  worm  wheel  support 
in  such  a  manner  that  the  rotating  prism  supporting  sleeve  with 
rotating  holder  can  be  removed.  The  rotating  prism  pinion  with 
rotating  head  pinion  can  now  be  removed.  Do  not  remove  the 
rotating  prism  from  the  rotating  prism  holder. 

137.  To  disassemble  the  deflection  mechanism. — Remove  the  de- 
flection dial  by  loosening  the  locking  screw,  drive  out  the  taper  pin 
from  the  worm  knob,  unscrew  the  worm  knob  from  the  end  of  the 
deflection  worm;  the  compensating  spring  can  now  be  removed. 
The  deflection  worm  can  be  withdrawn  by  turning.  Remove  the 
two  deflection  worm  wheel  support  screws  which  release  the  deflection 
worm-wheel  support,  remove  the  deflection  worm-wheel  and  sup- 
porting ring  and  deflection  worm-wheel  support  from  the  upper  end 
of  the  shank,  loosen  the  deflection  worm  bushing  clamp  plug  screw 
which  releases  the  deflection  worm  bushing  ^lamp  plug,  and  re- 
move the  deflection  worm  bushing. 

138.  To  remove  the  objective  lens. — Take  out  four  elbow  retaining 
screws,  unscrew  the  elbow  from  the  shank,  take  out  two  objective 
ceU  retaining  screws,  and  unscrew  the  objective  lens  cell.  Do  not 
attempt  to  remove  the  lens  from  its  cell.     With  the  objective  lens 

9950—17 i 


50 

cell  and  the  eyepiece  removed,  the  lower  reflecting  prism  may  be 
cleaned.  For  this  purpose  the  elbow  covers  should  be  removed  and 
the  back  surfaces  as  well  as  the  faces  of  this  prism  should  be  cleaned. 

WELDON    RANGE   FINDERS. 
(See  Pamphlet  No.  1908  and  Drawing  22-1-41.) 

139.  In  the  Weldon  range  finder,  accurately  ground  and  polished 
prisms  are  held  in  a  metal  frame.  The  prisms  should  not  be  removed 
for  any  purpose,  and  care  should  be  taken  not  to  disturb  them  in  their 
mounting,  as  with  the  range  finder  rigidly  held  vertical  the  prisms 
are  so  located  by  optical  tests  as  not  to  displace  the  image  from  the 
horizontal  plane  of  the  object.  In  case  adjustment  of  prisms  is 
required,  it  should  be  done  only  by  an  experienced  workman  with 
a  complete  set  of  working  fixtures  and  tools. 

140.  In  order  to  secure  the  maximum  intensity  of  illumination,  the 
refracting  surfaces  should  be  kept  clean  and  free  from  moisture, 
finger  prints,  etc.  The  silvered  surface  of  a  prism  requires  no  atten- 
tion. In  case  after  careful  cleaning  the  image  is  poorly  illuminated, 
the  range  finder  should  be  sent  to  an  arsenal  for  resilvering  the  prisms 
or  for  other  repairs. 

141.*  Methods  of  assembling  prisms. — The  Weldon  range  finders  at 
present  in  the  service  have  been  obtained  from  various  sources  and  at 
different  times,  and  they  differ  sUghtly  in  dimensions,  means  of 
securing  prisms,  and  in  other  minor  p)oints.  There  have  been  used 
three  general  methods  of  securing  prisms  in  place: 

(a)  By  cement. 

(6)  By  pins  or  plugs  let  into  the  prisms. 

(c)  By  clips  bent  over  edges  of  the  prisms  when  their  presence  does 
not  affect  the  field  of  view. 

(a)  Where  cement  has  been  used,  as  for  instance,  either  sodium 
silicate  or  sealing  wax,  immersing  the  range  finder  complete  in  cold 
water  and  gradually  raising  the  temperature  to  the  boiling  point  will 
ultimately  loosen  the  cement  and  allow  removal  of  the  prism.  The 
time  required  by  this  process  depends  upon  the  quality  and  condi- 
tion of  the  cement  used.  Frequently  an  hour  or  more  is  required  to 
loosen  the  prisms. 

(b)  Where  pins  or  screws  have  been  let  into  the  prisms,  cement 
may  also  have  been  used  to  aid  in  securing  these.  When  screws  have 
been  used  it  will  frequently  be  found  that  the  screw  head  has  been 
filed  away.  It  will,  therefore,  be  necessary  in  this  case  to  make  a 
new  slot  in  the  remaining  part  of  the  screw.  Then  loosen  all  cement 
as  above  described  and,  using  a  small  screw  driver,  turn  the  screw 
out.    This  sometimes  proves  to  be  a  very  difficult  operation. 

♦  See  paragraph  11. 


51 

(c)  Where  clips  are  used  the  screws  seeming  the  lower  clips  should 
be  removed.  The  prisms  may  then  be  removed  from  their  seats 
without  trouble.  The  upper  clips,  soldered  to  the  projecting  rings, 
need  not  be  removed. 

142.  No  special  tools,  other  than  small  screw  drivers,  pinchers,  etc., 
are  needed.  The  prisms  should  be  handled  carefully  and  inserted 
and  removed  by  the  fingers,  except  in  extreme  cases,  when  a  wooden 
wedge  or  stick,  carefully  used,  may  be  needed  to  remove  tightly  fitted 
prisms. 

143.  The  latest  method  adopted  for  securing  prisms  in  the  Weldon 
range  finder  is  by  clips  and  is  shown  in  the  plate.  This  method  is 
believed  superior  to  any  other  yet  devised  and  is  simple  in  application. 
Cement  is  no  longer  used,  as  it  is  liable  to  deterioration,  with  loss  of 
prism. 

144.*  Having  removed  the  prisms  from  the  case  for  resilvering  or 
other  repair,  to  reassemble,  proceed  as  follows:  Prepare  the  prism 
seat  so  that  it  will  receive  the  prism  snugly.  Three  small  steel 
blocks,  cut  accurately  to  the  dimensions  of  the  prism,  should  be 
prepared.  These  small  steel  blocks  are  used  in  adjusting  the  clips, 
as  they  will  sustain  the  pressure  required  in  bending  or  otherwise 
fitting  the  chps,  whereas  the  prisms  would  crack  or  chip  under  this 
pressure.  The  upper  clips  shown  on  the  plate  are  fu^t  soldered  to  the 
case.  They  should  then  be  bent  over  the  steel  blocks  to  give  a  snug  fit. 
The  lower  chps  shown  are  secured  by  screws  after  the  upper  clips 
have  been  adjusted  and  the  prisms  seated.  A  thin  piece  of  paper 
under  each  prism  will  be  found  useful  as  a  buffer  for  the  silvered  face 
in  fitting  the  prism  securely  in  its  seat. 

By  a  snug  fit  is  meant  a  fit  so  close  that  any  looseness  or  shaking 
is  prevented,  and  yet  not  so  close  that  undue  pressure  is  brought  to 
bear  on  the  prism  by  the  chps.  If  undue  pressure  is  brought  to  bear 
on  the  prism,  the  effect  will  be  to  warp  the  transmitted  rays  slightly 
and  thus  shghtly  blur  the  target  seen  through  the  prism. 

145.*  The  tolerance  permitted  in  the  angles  of  prisms  for  Weldon 
range  finders  is  ±  three  minutes  measured  as  the  error  of  the  angle 
through  which  a  ray  is  deflected  from  the  specified  angle.  By  careful 
grouping  of  such  prisms,  range  finders  are  made  in  which  the  range 
error  for  either  the  first  two  prisms  grouped  together,  or  the  last  two 
grouped,  does  not  exceed  ±  1  per  cent  of  the  range.  In  testing  and 
adjusting,  a  prism  must  be  held  or  located  so  as  not  to  displace  the 
image  from  the  horizontal  plane  of  the  object. 

xllthough  of  apparently  simple  construction  great  care  is  required 
in  the  testing  and  adjusting  of  prisms  of  this  range  finder.  If  prisms 
are  removed  for  resilvering  or  other  repairs,  a  fixture  should  be  pro- 
vided to  hold  the  range  finder  vertically,  and  a  telescope  should  bo 


*  See  paragraph  11. 


52 

used  in  locating  the  prisms.  Each  prism  should  be  so  adjusted  that 
for  the  range  finder  held  vertically  the  object  and  image  are  in  the 
same  horizontal  plane.  Care  should  be  taken  not  to  mix  the  prisms 
originally  assembled  in  a  given  range  finder,  as  they  are  not  inter- 
changeable with  similar  prisms  from  other  range  finders. 

FIELD   ARTILLERY   RANGE    FINDER,    1-METER    BASE. 

(See  pamphlet  No.  1796.) 

146.  Under  no  circumstances  shall  this  instrument  be  disassembled 
or  adjusted  except  by  the  manufacturer  or  by  an  arsenal  especially 
equipped  for  instrument  work. 

AIMING    CIRCLE,    MODEL   OF    1916. 
(See  Plate  L  herewith,  Pamphlet  No.  1796  and  Drawings  22-41-1  to  7,  inclusive.) 

147.  The  optical  parts  of  the  aiming  circle  should  not  be  removed 
unless  it  is  absolutely  necessary.  When  the  instrument  leaves  the 
manufacturer  all  the  joints  are  sealed,  and  the  breaking  of  this  seal 
allows  dust  and  moisture  to  enter.  In  case  disassembling  is  neces- 
sary, reassembling  should  be  done  in  the  reversed  order. 

148.  To  disassemble  the  eyepiece. — Take  out  the  eyepiece  retaining 
screw,  unscrew  the  eyepiece,  which  carries  with  it  when  assembled 
the  eye  lens,  the  field  lens,  and  the  reticule.  Unscrew  the  reticule 
cell  but  do  not  disturb  the  reticule.  Unscrew  the  eyepiece  cell 
which  contains  the  eye  lens  and  the  field  lens.  To  remove  the  lenses 
from  the  cell,  unscrew  the  lens  nut,  remove  the  field  lens,  take  out 
the  lens  separator,  and  remove  the  eye  lens. 

149.  To  dean  the  elbow  prism  and  erecting  prism. — Take  out  the 
elbow  cover  retaining  screw,  unscrew  the  elbow  cover,  take  out  the 
two  erecting  prism  holder  screws,  and  withdraw  the  erecting  prism 
holder.  Care  should  be  taken  not  to  disturb  the  prisms  when 
cleaning. 

150.  To  clean  the  objective  prism  or  the  objective. — ^The  telescope 
must  be  dismantled. 

151.  To  disassemble  the  elevation  mechanism. — Drive  out  taper  pin 
from  worm  knob,  remove  worm  knob  and  take  out  bearing  cap 
retaining  screw,  unscrew  bearing  cap,  and  withdraw  elevation  worm 
by  turning.  This  allows  the  telescope  elbow  to  be  removed  after 
the  five  objective  prism  housing  screws  have  been  unscrewed.  Take 
out  the  six  shutter  guide  screws,  slide  the  shutter  guides  with  the 
shutter  to  the  left-hand  side  and  take  out  five  objective  prism  hous- 
ing screws;  withdraw  the  angle  of  site  mechanism  which  allows  the 
objective  prism  housing  to  be  removed.  Do  not  attempt  to  remove 
the  prism  from  the  housing. 


53 

152.  To  remove  the  objective. — Unscrew  the  objective  lens  cell  nut. 
Scratch  a  line  on  the  eccentric  washer  and  objective  lens  ceU  before 
removing  them.     Do  not  remove  the  objective  from  its  cell. 

153.  To  disassemhle  the  angle  of  site  mechanism. — Loosen  angle  of 
site  dial  locking  screw,  drive  out  taper  pin  from  worm  knob,  remove 
worm  knob  and  take  out  bearing  cap  retaining  screw,  unscrew  bear- 
ing cap,  and  withdraw  the  angle  of  site  worm  by  turning.  Take  out 
the  three  level  vial  holder  screws,  remove  the  level  vial  holder,  take 
out  the  three  worm  wheel  holding  disk  screws,  and  remove  the  worm 
wheel  holding  disk  and  angle  of  site  worm  wheel. 

154.  To  disassemhle  the  azimuth  worm  mechanism. — Loosen  the  azi- 
muth worm  knob  locking  screw  and  remove  the  azimuth  worm  knob 
and  the  lever  spring;  take  out  the  azimuth  worm  lever  screw  and 
remove  the  azimuth  worm  lever.  The  azimuth  worm  may  now  be 
withdrawn  by  turning,  then  remove  the  azimuth  worm  bushing  and 
bushing  spring. 

155.  To  disassemhle  the  compass  inechanism. — Unscrew  the  cover 
ring  and  hft  the  glass  cover  with  parts  assembled  thereto  from  the 
instrument.  Take  out  the  three  level  housing  screws  and  remove 
the  level  housing.  Take  out  the  three  needle  release  guide  plate 
screws  and  remove  the  needle  release  guide  plate  (lower),  unscrew 
the  needle  release  button  and  remove  the  spring.  The  needle  release 
guide  plate  (upper)  and  the  needle  release  guide  plate  (lower)  may 
now  be  separated  and  removed  from  the  glass  cover.  Do  not  attempt 
to  disassemble  the  level  unless  the  fluid  has  leaked  out  to  such  an 
extent  as  to  require  refilling. 

156.  To  remove  the  compass  needle  from  the  needle  release  guide 
plate  (lower). — L^nscrew  the  needle  release  collar. 

SEXTANT   TELEMETER,    MODEL   OF   1911,    TYPE    A. 

(See  pamphlet  No.  1796.) 

(See  Plate  I.) 

157.  To  disassemhle  the  worm. — If  for  any  purpose  it  is  necessary  to 
remove  the  worm,  rotate  the  worm  until  the  worm  wheel  is  brought 
up  to  the  stop  plunger,  draw  back  the  stop  plunger,  and  continue 
rotation  of  the  worm  wheel  until  it  and  the  movable  mirror  are  clear 
of  the  worm  box.  Then  unscrew  the  four  worm-box  cap  screws  and 
draw  out  the  worm-box  cap  with  worm,  etc.  To  disassemble,  loosen 
the  worm  locking  screw, unscrew  the  retaining  nut,  using  teat  wrench 
No.  105,  and  draw  off  the  micrometer  head  and  worm  box  cap.  To 
remove  the  worm  from  the  worm  box,  first  remove  the  worm  plunger 
screw  and  then  the  worm  plunger  and  worm  plunger  spring.  Then 
push  the  worm  and  worm  bearing  out  of  the  worm  box,  applying  slight 
pressure  on  the  end  from  which  the  micrometer  was  removed,  clean. 


54 

lightly  oil  with  clock  oil  all  bearing  surfaces,  except  the  worm  teeth, 
which  should  be  lightly  coated  with  vaseline.  Reassemble  in  the 
reversed  order.  Take  special  care  that  no  dirt  or  grit  remaias  en 
any  bearing  surface.  Adjust  the  retaining  nut  to  remove  all  longi- 
tudinal play  and  readjust  the  niicrometer  scale  of  the  micrometer. 

158.  To  disassemble  tlie  cover. — Remove  the  two  fixed  mirror-holder 
screws  holding  the  fixed  mirror  holder  to  the  cover.  Rotate  the  worm 
imtU  the  clinometer  scale  registers  6,  draw  back  the  stop  plunger  and 
continue  rotation  of  the  worm  wheel  a  few  revolutions  in  the  same 
direction.  Remove  the  optical  square  body  from  its  seat  in  the 
cover.  Move  the  pendulum  until  its  toe  is  about  }  inch  from  the 
post  opposite  the  pendulum  lock.  Unscrew  the  four  cover  screws 
and  lift  the  cover.  Revolve  the  worm  wheel  until  disengaged 
from  the  worm  and  remove  worm  wheel  and  pendulum  assembled. 
Then  slip  the  pendulum  arms  over  the  worm  wheel  and  remove  the 
index  dial. 

1 59.  To  disassemble  the  pendulum. — Bend  the  pendulum  arm  inward 
to  release  the  spring  lock  and  push  the  arm  through  the  undercut 
groove  of  pendulum  weight.  After  removal  of  both  arms  the  pen- 
dulum prism  and  prism  spring  may  be  pushed  from  their  seat.  To 
remove  the  pendulum  lens  cell,  take  out  the  pendulum  lens  screw  and 
unscrew  the  cell.  As  all  its  joints  are  sealed  with  litharge  cement 
the  pendulimi  weight  should  be  disassembled  only  when  repairs  are 
required. 

160.*  Notes  on  adjustment. — The  pendulum  lens  is  adjusted  so  that 
its  focal  plane  lies  in  the  exposed  surface  of  the  pendulum  prism  on 
which  is  etched  a  reference  line.  The  telescope,  which  is  focused  for 
an  object  about  a  mile  distant,  is  placed  in  the  axes  of  the  pendulum 
lens  and  the  lens  cell  is  screwed  in  or  out  until  the  reference  line  on 
the  prism  is  seen  sharply  defined  by  the  telescope.  This  position  is 
noted  and  a  ring  is  made  to  fit*  between  the  upper  surface  of  the  pen- 
dulum weight  and  the  flange  of  eye  lens  cell.  A  set  screw  is  also 
inserted  in  the  cell.  In  final  assembling  all  exposed  joints  of  the 
parts  are  lightly  coated  with  htharge  cement  for  sealing. 

Before  assembling  in  the  instrument  the  pendulum  is  suspended 
by  its  arms  and  the  position  of  the  balancing  screw  in  the  pendulum 
weight  is  adjusted  until  the  front  face  of  the  pendulum  is  inchned 
11°  15'  from  the  plumb. 

161.*  A  coating  of  htharge  cement  is  placed  on  the  back  of  the 
movable  mirror  after  silvering.  The  mirror  is  then  placed  in  the 
movable  mirror  holder  and  the  ends  of  the  holder  are  burnished  over 
the  mirror.  The  mirror  and  the  holder  are  assembled  in  the  worm 
wheel  and  secured  by  burnishing  the  worm  wheel  lightly  over  the 
sides  of  the  mirror.     In  this  operation  care  must  be  taken  not  to 

*  See  paragraph  11. 


strain  the  mirror,  otherwise  the  definition  of  the  optical  system  will 
be  impaired.  The  space  between  the  mirror  holder  and  the  worm 
wheel  is  then  filled  with  a  mixture  of  litharge  cement,  whiting,  and 
lamp  black  mixed  to  the  consistency  of  soft  putty. 

162.*  After  the  optical  systems  are  assembled  the  telemeter  is 
placed  on  a  plane  horizontal  surface,  cover  up,  the  movable  mirror 
is  set  for  vertical  coincidence  of  the  images  formed  by  direct  and 
reflected  pencils,  and  the  fixed  mirror  holder  is  rocked  on  a  hori- 
zontal axis  by  means  of  the  four  fixed  mirror  screws  which  enter 
the  frame  and  the  two  fixed  mirror  adjusting  screws  which  bear 
against  the  frame  imtil  horizontal  lines  of  the  two  images  are  coinci- 
dent. Either  the  upper  or  the  lower  bearing  surface  of  the  mirror 
holder  should  be  in  contact  throughout  its  length  with  the  fixed 
mirror  seat  of  the  frame.  The  index  is  then  adjusted  so  that  while 
the  two  images  of  objects  about  a  mile  distant  are  in  coincidence,  the 
reference  line  on  the  index  is  opposite  the  0  graduation  of  the  index 
dial.  The  micrometer  scale  is  then  set  to  register  0.  The  telemeter 
is  then  placed  on  end  on  a  horizontal  surface  with  the  microm- 
eter above,  the  movable  mirror  is  rotated  to  register  3  centitoes 
elevation,  and  the  telescope  is  directed  on  a  target  at  any  distance 
in  the  same  horizontal  plane  as  the  axis  of  the  telescope.  The  pen- 
dulum is  then  released  by  throwing  the  pendulum  lock,  and  the 
adjusting  screw  in  the  pendulum  weight  is  adjusted  so  that  the 
image  of  the  reference  line  is  superposed  upon  the  image  of  a  hori- 
zontal line  i  mil  above  the  target.  The  telemeter  is  then  disas- 
sembled, a  dowel  pin  is  added  to  hold  the  index  in  its  proper  place, 
and  a  hole  is  drilled  and  a  pin  driven  through  the  adjusting  screw 
and  pendulum  weight.  The  allowance  made  in  the  adjustment  of 
the  pendulum  weight  compensates  for  the  loss  of  weight  resulting 
from  the  insertion  of  the  pin.  The  telemeter  is  then,  reassembled  for 
final  adjustment  of  the  fixed  mirror  for  coincidence  of  horizontal 
lines  and  for  the  setting  of  the  scale  at  0  when  the  images  formed  by 
the  direct  and  the  reflected  pencils  from  distant  objects  are  coincident. 

163.  In  subsequent  adjustments  after  repairs  the  fixed  mirror  may 
be  rotated  on  its  vertical  axis  to  bring  the  images  of  a  distant  object 
into  coincidence  when  the  index  registers  0  on  the  index  dial.  After 
setting  the  fixed  mirror  the  final  adjustment  for  coincidence  of  vertical 
lines  of  images  is  made  by  rotating  the  movable  mirror  for  coincidence 
of  images  and  then  adjusting  the  micrometer  scale  to  register  0.  In 
this  case  a  rebalancing  of  the  pendulum  will  be  required.  The 
accuracy  of  both  the  telemeter  and  the  clinometer  systems  are  tested 
by  comparisons  with  graduated  circles. 

*  See  paragraph  11. 


56 
GEARED  INSTRUMENTS   (Group  b). 

164.  Gearing. — Loss  of  adjustment  and  lack  of  accuracy  due  to 
gearing  is  ordinarily  made  apparent  by  what  is  known  as  backlash, 
lost  motion,  or  looseness.  This  looseness  develops  either  from  the 
actual  wear  of  the  parts  which  mesh  together  or  from  the  loss  of  posi- 
tion and  looseness  of  surrounding  parts,  which  should  keep  the  gears 
in  close  contact.  Thus,  taking  the  range  quadrant  and  rear  sight  of 
the  8-inch  field  materiel  as  examples,  the  pinions,  quadrant-arm 
racks,  and  scroll  gear,  worms,  etc.,  are  from  the  very  nature  of  their 
service  subjected  not  only  to  constant  wear,  but  to  constant  wear 
under  the  severest  conditions  of  weather,  dust,  grit,  etc.  The  close 
mesh  and  fit  of  these  parts  will  deteriorate,  and  this  deterioration 
sometimes  proceeds  very  rapidly.  When  possible,  if  new  parts  are 
not  available  and  the  demands  of  the  service  prevent  the  return  of 
the  part  affected  for  repair,  a  thin  washer,  an  added  bushing,  or  otheif 
similar  slight  repair  wiU  tide  over  the  difficulty.  But  when  th6 
looseness  developed  is  so  great  as  to  destroy  the  value  of  the  instru- 
ment, new  gears,  worms,  etc.,  must  be  cut,  and  the  parts  refitted 
and  adjusted.  For  service  in  the  field  it  should  be  remembered  that 
instruments  issued  from  the  Frankford  Arsenal  have  corresponding 
parts  of  the  same  model  interchangeable.  Thus  a  good  part  of  one 
otherwise  unserviceable  instrument  may  be  taken  and  used  for 
another  instrument,  when  such  exchange  is  necessary.  Rear-sight 
brackets,  shank  sockets,  shank,  etc.,  may  thus  be  interchanged. 

165.  Where  the  looseness  has  developed  from  the  loss  of  position 
of  surrounding  parts  which  should  keep  the  gears  in  close  contact, 
as,  for  instance,  in  the  case  of  the  gun  azimuth  subdial  mechanism 
in  the  Whistler-Hearn  plotting  board,  the  dial  box  in  which  the 
mechanism  is  housed  should  be  moved  closer  up  to  the  movable  limb 
and  resecured  by  the  screws  provided.  If  backlash  exceeding  0.03° 
is  still  found,  the  gears  themselves  or  their  bearings  should  be  exam- 
ined for  dust  or  dirt.  Careful  cleaning  of  such  parts  will  frequently 
remove  a  cause  of  error  in  the  readings  obtained.  The  worm  stand 
of  plotting  boards  may  be  similarly  adjusted. 

166.  On  those  instruments  in  which  a  worm  and  worm  gear  are 
employed  to  obtain  rotation  in  horizontal  or  vertical  planes,  adjust- 
ments are  provided  to  remove  longitudinal  play  between  the  worm 
and  worm  bearing  and  to  remove  backlash  between  the  worm  and 
worm  gear.  To  remove  longitudinal  play,  turn  up  the  screw  or  nut 
on  the  end  of  the  worm  until  there  is  no  longitudinal  shake  of  the 
worm,  but  the  worm  should  revolve  freely  when  disengaged  from  the 
worm  gear.  The  worm  is  ordinarily  held  in  mesh  with  the  gear  by  a 
flat  spring.  The  pressure  of  the  worm  on  the  gear  is  regulated  by 
an  adjusting  screw.     This  adjusting  screw  should  be  set  at  the  critical 


57 

position  at  which  there  is  no  backlash  between  worm  and  gear  and 
the  pressure  of  the  worm  against  the  spindle  is  a  minimum  for  no 
backlash. 

167.  Care  should  be  taken  to  keep  the  gears  of  instruments  clean 
and  lightly  oiled.  The  cutting  of  worms  and  gear  sufficiently  accurate 
for  instrument  use  is  a  difficult  machine  operation,  and  the  accuracy 
of  such  parts  can  be  preserved  only  by  careful  handling,  cleaning, 
and  adjusting  these  parts  in  service. 

168.  Test  of  levels. — Levels  furnished  with  instruments  are  ordi- 
narily adjustable,  although  the  open  sights  and  range  quadrants  for 
mobile  artillery  and  the  mortar  quadrants  contain  nonadjustable 
levels,  which  are  rigidly  held  in  a  metal  casing  or  tube  and  are  accu- 
rately adjusted  and  tested  by  the  manufacturer  and  do  not  require 
adjustment  by  the  service.  Adjustable  levels  are  of  two  types — one 
adjusted  by  exposed  adjusting  screws  as  the  levels  on  the  base  of  an 
azimuth  instrument  or  of  a  battery  commander's  telescope;  the  other 
adjusted  by  internal  screws,  to  reach  which  a  cap  must  be  removed 
from  the  level  box,  as  in  the  case  of  the  cross  level  on  the  range  quad- 
rant and  the  elevation  level  on  the  rear  sight  for  3-inch  field  materiel. 
Both  types  of  adjustable  levels  are  accurately  adjusted  and  tested  by 
the  manufacturer,  but  these  levels  are  designed  for  and  will  require 
adjustment  by  the  service. 

169.  In  case  of  breakage  or  looseness  of  level  vials  belonging  to 
instruments,  the  metal  case  surrounding  the  level  vial  must  be 
opened,  and  in  case  of  a  broken  vial  the  broken  parts  and  old  packing 
must  be  removed.  A  level  of  the  same  degree  of  sensitiveness  as 
that  originally  in  the  instrument  should  be  obtained.  The  level 
vial  mixture  should  be  specified  as  60  per  cent  alcohol  and  40  per 
cent  ether.  Levels  differ  in  sensitiveness,  depending  upon  the  accu- 
racy demanded  in  the  instruments  with  which  they  are  used.  Thus 
the  large  striding  level  for  the  Swasey  depression  position  finders 
shows  a  movement  of  the  bubble  of  -^  inch  for  a  variation  in  level 
of  15  seconds  of  arc;  the  level  for  the  gunner's  quadrant  shows  a 
movement  of  the  bubble  of  y?  inch  for  a  variation  in  level  of  5  minutes 
of  arc;  the  Weldon  range-finder  level  is  simply  a  general  leveling 
device  for  an  instrument  held  in  the  hand,  subject  to  constant  vibra- 
tion, and  hence  is  not  sensitive;  any  good  commercial  vial  of  the  size 
needed,  not  specially  ground,  but  in  which  the  highest  point  for 
bubbles  is  easily  determined  and  symmetrically  placed,  will  do  for 
this  use.  Levels  in  which  the  ^^^-inch  graduation  is  to  show  a 
certain  variation  in  minutes  or  seconds  of  arc  must  have  the  interior 
surface  of  the  vial  specially  ground  to  the  correct  radius  of  curvature 
Such  levels  before  acceptance  should  be  tested  on  a  regular  level-test- 
ing machine.  If  one  of  them  is  not  available,  a  Y  block  properly 
mounted  to  receive  the  level,  terminating  in  standards  which  can  h( 


58 

raised  or  lowered  definite  amounts  by  screw  action,  and  from  which, 
knowing  the  pitch  of  the  screw,  etc.,  the  angle  to  which  the  Y  block 
is  tilted  ma}'  be  determined,  can  be  used  in  ascertaining  the  move- 
ment of  level  bubbles  corresponding  to  a  certain  angular  displace- 
ment. Levels  must  be  ground  so  that  the  movement  of  the  bubble 
over  the  length  of  the  graduations  on  the  vial  is  uniform. 

170.  Adjustment  of  levels. — Having  tested  the  level  vial  for  sensi- 
tiveness and  uniformity,  place  paper  or  cotton  packing  in  the  bottom 
of  the  metal  level  holder,  so  that  the  level  will  fit  snugly.  Care  must 
be  taken  not  to  pack  the  level  too  tightly,  as  a  very  tightly  packed 
level  vial,  exposed  to  extreme  variations  of  temperature,  will  probably 
crack.  On  the  other"  hand,  when  the  level  is  not  packed  sufficiently, 
it  will  readily  change  in  position  and  thus  not  remain  true.  Having 
determined  the  proper  amount  of  packing,  by  inserting  and  removing 
the  level  frequently  until  the  right  fit  is  found,  pack  the  ends  of  the 
level  to  prevent  longitudinal  motion  in  the  case,  using  cotton  or  a 
slight  amount  of  plaster  of  paris  (dental  plaster  which  will  set  in 
from  5  to  10  minutes),  then  screw  on  the  level  holder  end  caps  or  top, 
as  the  case  may  be.  As  an  example  illustrating  the  principles  of  level 
adjustment,  take  the  striding  level  of  the  Swasey  depression-position 
finder,  Type  Al.  Prepare  a  carefully  turned  cylindrical  block, 
mounted  on  a  small  pedestal  or  base  provided  with  a  leveling  attach- 
ment, as  three  screws  at  the  vertices  of  an  isosceles  triangle.  Place 
the  striding  level  on  the  cylindrical  block  and  bring  the  bubble  to  the 
center  of  the  scale  by  means  of  the  leveling  screws  of  the  pedes taj  of 
the  cylindrical  block.  Then  lift  the  level  from  the  cylindrical  block 
and  turn  it  around  so  that  the  former  right  end  will  become  the  left 
end,  and  place  again  on  the  cylindrical  block.  If  the  level  is  properly 
adjusted,  the  bubble  will  still  be  in  the  center  of  the  scale.  If  the 
level  is  not  properly  adjusted,  correct  for  half  of  the  bubble  error  by 
the  small  screws  at  either  end  of  the  level  vial  case,  and  for  the  other 
half  of  the  error  by  the  leveling  screws  of  the  pedestal.  Then  reverse 
the  striding  level  as  before,  and  continue  this  process  until  the  bubble 
shows  no  variation  after  reversal,  when  the  striding  level  will  be 
properly  adjusted. 

171.  The  following  additional  examples  of  specif  cases  are  given 
as  containing  such  remaining  information  on  the  principles  of  level 
adjustment  as  may  be  necessary.  The  adjustment  of  the  elevation 
or  angle  of  site  level  for  the  range  quadrant  of  the  3-inch  field  materiel 
is  made  as  follows:  After  carefully  packing  the  level  and  closing 
vial  holder,  the  zero  mark  on  the  holder  is  brought  opposite  the 
reference  number  (3)  on  the  level  scale  by  means  of  the  clinometer 
level  screw.  (See  plate  and  description  of  ''Range  quadrant"  in 
pamphlet  No.  1659,  ''Handbook  of  the  3-inch  Field  Artillery 
Materiel.")     The  micrometer  disk  is  then  loosened,  by  releasing  its 


59 

retaining  screw,  and  is  turned  until  the  zero  mark  on  the  scale  is 
brought  opposite  the  zero  or  index  mark  on  the  quadrant  body. 
The  retaining  screw  is  then  tightened,  when  these  parts  will  be  in 
adjustment  for  range. 

172.  The  transverse  or  cross  level  of  the  range  quadrant  is  adjusted 
as  follows:  The  cross-level  vial  is  first  secured  in  its  tube  and  then 
inserted  in  the  level  holder.  One  end  of  the  tube  containing  the 
level  vial  fits  snugly  in  the  level  holder.  The  other  end  of  the  tube 
is  somewhat  smaller  and  contains  four  radial  adjusting  screws.  The 
verticality  of  the  rocker  arm  should  be  determined  by  the  testing 
level  or  by  a  steel  square  projecting  from  a  horizontal  plate  in  such 
manner  that  the  base  of  the  square  will  rest  on  the  plate  when  the 
vertical  edge  is  in  contact  with  the  planed  surface  of  the  rocker  arm 
or  parallel  to  it.  The  level  should  be  adjusted  by  means  of  the 
upper  and  lower  radial  screws  for  this  position  of  the  rocker  arm. 
Then  by  means  of  the  two  side  radial  screws  the  level  vial  and  tube 
should  be  adjusted  in  the  level  holder,  so  that  the  bubble  remains 
central,  while  either  the  quadrant  or  the  body  is  moved  in  a  vertical 
plane. 

173.  The  following  detailed  instructions  for  the  disassembling  of 
bases  of  some  of  the  more  complex  instruments  are  given  below.  No 
instrument  should  be  disassembled  except  when  required. 

BATTERY   COMMANDER'S    TELESCOPE,    MODEL   OF    1905. 
(See  Plate  E.) 

174.  To  disassemhle  the  center  and  the  worm  mecMnism. — Remove 
the  platen  caps  (4DA)  and  lift  out  the  telescope.  Do  not  remove  the 
four  spindle  screws  (2B).  The  spindle  should  not  he  removed  from  the 
platen.  Remove  the  one  spindle-nut  screw  (2C)  and  the  spindle  nut 
(2J),  using  teat  wrench.  No.  41.  'Throw  the  azimuth  worm  out  of 
mesh,  loosen  the  slow-motion  screw,  and  lift  the  platen  (4R)  with 
spindle  (2A)  and  the  horizontal  hmb  (4B)  from  the  fixed  limb  (2W) 
carefully,  to  avoid  bruising.  Unclamp  the  slow  motion  clamp  screw 
and  remove  the  slow-motion  arm  (3E).  Remove  the  platen  cover 
(4FA) .  After  taking  off  the  worm  box  stud  nut  (4AA)  and  unscrew- 
ing the  azimuth  worm  box  stud  (4M) ,  lift  the  azimuth  worm  mechan- 
ism from  the  platen  (4R).  Remove  the  azimuth  worm  adjusting 
screw  (4U) ,  loosen  the  dial  nut  screw  (4 JA) ,  and  remove  the  dial  nut 
(4Y),  the  two  azimuth  dial  screws  (4SA),  and  washers  (4UA). 
Remove  the  azimuth  micrometer  head  (4K)  and  the  azimuth  dial 
(4NA)  and  push  the  azimuth  worm  from  its  bearing. 

Drive  out  the  eccentric  crank  pin  (2V)  and  drive  iii  eccentric  (2T) . 
The  eccentric  crank  (2U)  will  then  drop  off.  Reassemble  all  parts  in 
the  reversed  order.     Use  clock  oil  on  the  spindle  bearing. 


GO 

175.  To  disassemble  the  leveling  screws,  etc. — Screw  the  four  leveling 
screws  (3CA)  into  the  fixed  limb  to  remove  friction  between  the  level- 
ing plate  (3 A)  and  the  fixed  limb  nut  (2X).  Take  out  the  fixed  limb- 
nut  screw  (2M),  unscrew  the  fixed  limb  nut  (2X),  using  adjustable 
key  wrench  No.  37.  Lift  off  the  leveling  plate  (3A)  and  the  screw 
collar  (3D).  The  four  leveling  screws  (3CA)  may  then  be  removed 
from  the  fixed  limb  (2W)  and  the  shoes  driven  off  with  a  light  blow 
of  a  maUet. 

Remove  the  plunger  sleeve  screw  (3S),  unscrew  the  slow-motion 
plunger  sleeve  (3L)  from  the  fixed  limb.  The  slow-motion  plunger 
(3K)  and  slow-motion  plunger  spring  (3M)  may  then  be  separated 
from  the  slow-motion  plunger  sleeve. 

176.  To  remove  the  elvation  worm  mechanism. — Remove  the  two 
elevation  worm-box  studs  (4GA)  and  lift  off  the  worm  box.  Loosen 
the  dial-nut  screw  (4JA),  remove  the  dial  nut  (4Y),  the  two  elevation- 
dial  screws  (4TA)  and  the  screw  washers  (4UA).  Lift  off  the  eleva- 
tion dial  (4HA),  drive  out  the  elevation  worm  (4Z)  by  tapping 
ligh  tly  on  the  threaded  end  of  the  worm,  thereby  forcing  out  the  plug 
(4X)  and  releasing  the  elevation  micrometer  head  (4WA). 

AZIMUTH    INSTRUMENT,    MODEL   OF   1910.  ^ 

(See  Pamphlet  No.  1656  and  drawings  22-30-1  to  14,  inclusive.) 

177.^  To  disassemble  the  base. — Remove  the  azimuth  stop  (llT), 
unscrew  the  spindle-washer  screw  (9F)  and  lift  off  the  spindle  washer 
(1  ID).  Lift  off  the  body  (9A)  and  yoke  (lOA)  assembled  from  the 
azimuth  circle  (9B).  Remove  the  spindle-nut  lock  screw  (llAA) 
an  d,  using  adjustable  key  wrench  No.  36,  unscrew  the  spindle  nut 
(1  IC).  The  azimuth  circle  may  then  be  lifted  from  the  leveling 
plate  (lOP). 

To  remove  yoke  (lOA)  from  body  (9A)  take  out  the  yoke-washer 
screws  (lOT),  draw  off  yoke  washer  (llK)  and  separate  yoke  from 
body  and  azimuth  slow-motion  arm  (9D). 

178.  To  disassemble  worm. — Remove  the  yoke  and  the  body  from 
th  e  azimuth  circle.  Take  off  the  worm-box  cover  (9C).  Remove  the 
worm-shaft  screw  (lOV).  Draw  off  the  drum  crank  (lOL),  the  azi- 
muth drum  (lOG),  the  drum  adjusting  clamp  (lOJ),  and  drum 
adjusting  sleeve  (lOK)  assembled.  Loosen  the  azimuth-drum  cover, 
set  screw  (lOY)  and  pull  off  the  azimuth  drum  cover  (lOB). 
Unscrew  partially  the  worm-box  adjusting  screw  (8AC).  Remove 
the  worm-box  support  screws  (lOZ)  and  draw  out  the  worm-box 
support  (lOR).  Unscrew  the  worm-box  pivot  (8X)  and  draw  out 
the  worm  screw  (lOF)  and  the  worm  box  (lOH)  assembled.     Unscrew 

1  These  instructions  also  apply  to  the  azimuth  instruments,  models  of  1900  and  1900  Mi. 


(Jl 

the  worm-screw  bearing  screw   (lOAA),   pull  out   the  worm-screw 
bearing  (lOQ)  and  shp  out  the  worm  screw  (lOF). 

Use  clock  oil  on  all  internal  bearing  surfaces.  Assemble  all  parts 
in  the  reversed  order.  In  case  the  felt  strip  (IF)  becomes  unservice- 
able replace  it  by  a  good  grade  of  soft  felt  J  inch  thick. 

SWASEY   DEPRESSION    POSITION    FINDER.^ 

(See  pamphlet  No.  1875  and  drawings  22-22-1  to  15,  inclusive.) 

179.  To  disassemble  the  azimuth  worm  mechanism.. — Loosen  the 
azimuth  drum  lamp-bracket  screw  (14FB)  and  rotate  the  azimuth- 
drum  lamp  bracket  slightly.  Loosen  the  worm-box  pivot  screw 
(14YA)  and  unscrew  the  worm-box  pivot  (8Z).  Throw  the  worm 
out  of  mesh  and  pull  the  worm  box  assembled  down  out  of  its  seat. 
Remove  the  azimuth-drum  screw  (14M)  and  pull  off  the  azimuth 
drum  (8S).  Loosen  the  azimuth  drum-cover  screw  (14P)  and  remove 
the  azimuth  drum  cover  (8Q).  The  azimuth  drum  lamp  bracket  may 
also  be  disassembled.  Take  out  the  worm-box  adjusting  screw  (14U) 
and  the  worm-box  oil  tube  (8DA).  Push  out  the  worm  screw  (8B) 
and  the  worm-box  bush  (8C). 

In  assembling,  tighten  the  azimuth  drum  screw  (14M)  so  that  the 
worm  screw  may  revolve  in  the  worm  box  without  great  friction  and 
without  longitudinal  play.  Adjust  the  worm-box  adjusting  screw 
(14U)  so  that  the  worm  screw  comes  just  to  bearing  with  the  azimuth 
circle  and  operates  without  appreciable  backlash. 

180.  To  remove  the  range  yointer  arm  (9T). — Remove  the  range 
pointer  cover  (6P)  and  the  curvature  attachment  guard  (6F).  Un- 
screw the  two  range  pointer  screws  (14GA)  in  the  forks  of  the  range 
pointer  arm  (9T) .  Remove  the  screws  from  the  range  pointer  guides 
(9W)  and  (9X).  Pull  out  the  range  pointer  (9U)  and  the  range 
pointer  guides  (9W)  and  (9X).  Take  out  the  four  pointer  bracket 
cap  screws  (14AB)  and  remove  the  range  pointer  bracket  (9N). 
Loosen  the  pointer  arm  screw  (14B)  and  push  out  the  range  pointer- 
arm  shaft  (9Y).  When  reassembling,  note  that  a  flat  is  machined 
on  the  range  pointer-arm  shaft  (9Y)  for  the  set  screw. 

181.  To  remove  the  hell  cranlc  lever  (6D). — Remove  the  curvature 
attachment  guard  (6F).  Scribe  a  line  across  the  rack  on  the  beU 
crank  lever  and  the  worm  sleeve  (4AA)  for  reference  in  assembling. 
If  no  other  parts  are  to  be  disassembled,  take  care  that  the  range 
drum  is  not  moved  while  the  bell  crank  lever  is  disassembled.  If 
other  parts  are  to  be  disassembled,  the  instrument  should  be  set  for 
telescope  level  and  the  range  drum  removed  before  the  bell  crank 
lever  is  taken  off.  Remove  the  lever  post  caps  (7B).  Lift  off  bell 
crank  lever  assembled. 

1  The  nomenclature  given  is  for  the  type  All  instrument.    The  parts  of  this  instrument  will  be  disas- 
sembled only  in  case  of  necessity  for  making  repairs  or  correcting  errors,  etc. 


(ili 

182.  To  remove  the  range  drum. — If  the  range  pointer  arm  (9T)  is 
to  be  removed,  set  the  instrument  at  a  short  range  and  remove  the 
pointer  arm  screw  (14B)  from  the  hub  of  the  arm  (9T).  Then  revolve 
the  drum  until  it  indicates  telescope  level.  Note  that  in  this  position 
the  cam  crank  pin  (6E)  bears  on  the  flat  of  the  cam  (6T).  Remove 
the  range  pointer  cover  (6P).  Take  out  the  two  range  pointer  screws 
(14GA)  from  the  fork  of  the  range  pointer  arm  (9T)  and  the  screws 
from  the  range  pointer  guides  (9W)  and  (9X).  Pull  out  the  range 
pointer  (9U)  and  the  range  pointer  guides.  Remove  the  screws  hold- 
ing together  the  two  sections  of  the  range  drum  cover  (lOD)  and  (lOE). 
Remove  from  the  cradle  the  range  crank  (9K),  the  oiler  for  oiling  the 
range  crank  shaft  (9H),  and  the  oiler  for  lubrication  of  the  azimuth 
circle.  Take  out  the  large  drum-cover  screws  (14S)  holding  the  drum 
covers  to  the  cradle  (7D).  Pull  off  the  drum  covers.  Take  out  the 
three  screws  from  the  slotted  holes  in  the  range  drum  (9L)  and  remove 
the  range  drum  (9L).  Unscrew  the  drum  gear  screw  (14A)  and  pull 
off  the  range  drum  gear  (9E).  The  range  crank  pinion  (9D)  and 
range  crank  shaft  (9H)  may  now  bfe  removed.  No  attempt,  how- 
ever, should  be  made  to  remove  these  parts  until  after  the  range 
drum  gear  is  removed. 

183.  To  remove  the  cam  of  the  curvature  attachment. — Remove  the 
range  drum  and  gear  complete.  Note  instructions  in  paragraph  159 
above  regarding  setting  of  range  drum  before  it  is  removed.  Mark 
the  opposite  teeth  of  the  worm  shaft  pinion  (5T)  and  the  cam  shaft 
gear  (5U).  These  teeth  may  already  be  spot  marked.  Remove  the 
cam  bracket  caps  (5Q)  and  pull  out  the  cam  shaft  (4V),  cam  (6T), 
and  cam  shaft  gear  (5U)  assembled.  The  cam  and  cam  shaft  gear 
are  located  on  the  cam  shaft  (4V)  by  paper  pins.  The  cam,  cam 
shaft,  and  cam  shaft  gear  may  be  removed  after  the  curvature 
attachment  guard  (6F)  is  taken  off,  provided  that  a  bent  wire  is  used 
in  removing  the.  capstan  head  screws  holding  the  cam  bracket  caps 
(5Q).  If,  however,  other  parts  are  to  be  disassembled,  it  wiU  be 
preferable  to  remove  the  range  drum,  etc.,  first. 

184.  To  remove  the  range  drum  shaft. — Remove  the  range  drum 
(9L),  the  range  pointer  arm  (9T),  the  range  pointer  bracket  (9N), 
the  bell  crank  lever  (6D),  and  cam  shaft  with  cam  and  gear.  Note 
instructions  above  for  setting  of  the  range  drum  before  its  removal 
and  for  marking  the  opposite  teeth  of  the  worm  shaft  pinion  (oT) 
and  the  cam  shaft  gear  (5U),  and  for  marking  the  bell  crank  lever 
and  the  worm  sleeve.  Drive  out  the  taper  pin  and  remove  the  worm 
shaft  pinion  (5T).  Loosen  the  cam  bracket  screw  (5N).  Remove 
the  two  capstan  head  screws  holding  the  worm  sleeve  (4AA)  in  the 
cam  bracket  (5L),  the  filister  head  screw  holding  the  cam  bracket 
(5L)  to  the  cradle  (7D),  the  one  headless  locating  screw  locating  the 
worm  sleeve  (4AA)  in  the  cradle  (7D),  and  the  clamp  screw  (14BB) 


63 

from  the  cradle.  Pull  worm  sleeve  (4A*A)  to  the  rear,  slipping  from 
it  the  cam  bracket  (5L).  Loosen  the  set  screw  holding  the  worm 
sleeve  bush  (6C)  in  the  worm  sleeve  (4AA),  pull  out  the  range  drum 
shaft  (4Q),  and  remove  the  worm  sleeve  bush  (6C). 

Reassemble  in  reversed  order,  taking  care  to  mesh  gearing  to  the 
teeth  previously  marked,  to  locate  the  flat  on  the  smaller  end  of  the 
cam  uppermost,  and  to  assemble  the  bell  crank  lever  according  to  the 
mark  previously  scribed. 

185.  To  remove  the  cradle,  etc.,  from  the  base, — Take  out  the  oil  cup 
from  spindle  washer.  Remove  the  brush  block  (ISW).  Use  teat 
wrench  No.  43  and  unscrew  spindle  washer  (USA).  Then  lift  off 
the  cradle  (7D).  Four  men  are  required  for  this  work.  The  cradle 
must  be  lifted  directly  up  about  12  inches.  The  vertical  spindle 
(llJA)  is  driven  in  the  azimuth  circle  (8F)  and  should  not  be  removed. 
To  remove  the  azimuth  circle  (8F)  and  the  azimuth  plate  (7C)  loosen 
the  azimuth  drum  set  screws  (14CB)  and  lift  the  two  parts  off  the 
base  (7E).  Remove  the  spindle  nut  screw  (14ZA)  from  the  spindle 
nut,  unscrew  the  spindle  nut  (llRA)  and  lift  the  azimuth  circle  from 
the  azimuth  plate  (7C). 

One  leveling  shoe  (8K)  is  made  with  a  tongue.  The  position  of  this 
shoe  may  be  changed  without  disassembling  the  azimuth  circle  (8F) 
from  the  azimuth  plate  (7C). 

186.  Notes  on  assembling. — Assemble  the  range  drum  shaft  and 
the  worm  sleeve  bush,  etc.,  in  the  worm  sleeve  (4AA).  Slide  the 
worm  sleeve  and  cam  bracket  (5L)  in  their  seats,  locating  the  worm 
sleeve  by  the  headless  locating  screw,  and  put  in  the  screws  which  hold 
the  cam  bracket  and  clamp  the  worm  sleeve.  Assemble  in  the  cam 
bracket  (5L)  with  flat  of  cam  uppermost,  the  cam  shaft  (4V)  with  cam 
(6T)  and  cam  shaft  gear  (5U)  assembled.  Place  in  position  the 
crank  lever  noting  the  marks  previously  scribed.  If  no  marks  are 
scribed  on  it,  assemble  it  so  that  its  rear  end  just  clears  the  rear  lug 
of  cradle.  While  placing  the  bell  crank  lever  in  its  bearing  hold  up 
the  cam  crank  (5V)  so  that  the  cam  crank  pin  (6E)  does  not  touch  the 
cam.  In  this  position  of  the  cam  and  the  bell  crank  lever,  the  cam 
crank  pi'i  (6E)  should  rest  on  Ihe  flat  of  the  cam.  Assemble  the 
range  crank  pinion  (9D)  and  range  crank  shaft  (9H) . 

Then  assemble  the  range  drum  gear,  the  range  drum  at  telescope 
level,  and  the  pointer  mechanism.  The  range  pointer  arm  (9T) 
should  be  meshed  in  the  range  drum  shaft  so  that  the  pointer  indicates 
telescope  level.  Assemble  the  worm  shaft  pinion  as  marked  (if  not 
marked  assemble  for  trial) .  Rotate  parts  by  the  range  crank  to  prove 
that  the  range  drum  may  be  revolved  from  telescope  level  to  the 
shortest  range.  If  the  full  movement  can  not  be  obtained,  loosen 
the  four  pointer  bracket  cap  screws  (14AB)  and  shift  the  pointer 


"64 

bracket  on  the  worm  sleeve  to  obtain  it.     Assemble  the  pointer  arm 
screw  (14B)  with  the  range  drum  set  for  a  short  range. 

187.  To  test  adjustment} — Level  the  cradle,  set  the  range  drum  at 
telescope  level,  assemble  the  telescope  and  the  striding  level.  Adjust 
the  striding  level.  Set  the  telescope  level.  Adjust  the  cam  crank 
screw  (5W)  if  necessary  so  that  the  top  surface  of  the  carriage  crank 
(5P)  is  perpendicular  to  the  height  scale.  Slide  the  height  slide  (4E) 
assembled  along  the  rail  and  by  the  telescope  observe  any  external 
object.  If,  during  movement  of  the  height  slide,  the  image  shifts 
in  respect  to  the  cross  wires,  remove  the  plunger  (4P)  and  adjust  the 
plunger  screw  (4U)  in  the  plunger.  Replace  the  plunger  for  trial  and 
readjust  it  until  the  image  remains  stationary.  Level  the  telescope 
by  the  range  crank.  If  the  cam  crank  pin  (6E)  does  not  rest  on  the 
flat  of  the  cam  (6T) ,  remove  the  worm  shaft  pinion  (5T) ,  turn  the  cam 
shaft  until  the  pin  rests  there  and  reassemble  the  pinion.  Now  the 
movement  of  the  range  crank  has  thrown  the  guide  (12G)  out  of 
parallelism  with  the  rail  of  the  bell  crank  lever.  Readjust  the 
plunger  (4P)  until  there  is  no  movement  of  the  image  over  the  cross 
wires  when  the  height  slide  is  moved,  readjust  the  level  of  the  tele- 
scope by  the  range  crank  until  the  striding  level  indicates  level. 
Repeat  until  when  the  telescope  is  level  and  the  height  slide  may  be 
moved  without  changing  its  level.  Then  set  the  range  drum  to 
indicate  telescope  level. 

This  adjustment  may  be  made  with  the  use  of  the  Testing  Instru- 
ment described  in  Pamphlet  No.  1875.  In  this  case  observe  the 
rotation  of  the  telescope  by  means  of  the  testing  instrument  instead 
of  by  the  telescope. 

188.  To  set  the  height  scale. — After  adjusting  the  telescope,  the 
height  slide,  the  curvature  mechanism,  and  the  range  drum,  set  the 
drum  at  telescope  level  (the  telescope  being  level)  and  adjust  the 
testing  instrmnent  ^  to  register  0.  With  the  height  scale  set  for  the 
proper  height,  measure  the  angular  rotation  of  the  telescope  for 
various  setting  of  the  range  drum.  In  case  the  angles  measured  are 
greater  than  the  calculated  angles,  move  the  height  slide  to  register 
a  slightly  smaller  height  of  site.  Repeat  the  readings  and  readjust 
until  the  measured  angles  agree  with  the  calculated  angles.  Then 
adjust  the  height  scale  pointer  screw  (6V)  until  the  height  scale 
pointer  (llN)  registers  the  correct  height.  Loosen  the  screws  in  the 
pointer  stop  (IIP)  and  set  the  index  line  of  the  pointer  strip  opposite 
the  line  on  the  height  scale  pointer.  Make  this  adjustment  for  the 
mean  height  at  which  the  instrument  is  to  be  used. 

1  For  instructions  for  collimation  and  leveling  by  means  of  the  striding  level  see  paragraph  78, 
«  For  description  of  the  testing  instrument  and  instructions  for  its  use  see  Pamphlet  No.  1875  (Descrip* 
tton  of  the  Swasey  Depression  Position  Finders). 


65 

189.  To  determine  the  angular  error  of  the  instrument,  bring  the 
range  drum  to  register  the  specified  range  and  read  the  angle  of  rota- 
tion by  the  testing  instrument.  Subtract  the  observed  reading  from 
the  calcidated  angle  to  obtain  the  error.  If  it  is  desired  to  obtain 
the  error  in  yards,  set  the  testing  instrument  to  the  calculated  angle 
and  read  the  range  from  the  drum.  The  range  error  is  the  meas- 
ured range  subtracted  from  the  calculated  r|inge.  The  following  are 
calculated  values  of  the  angular  rotation  of  the  telescope  from  tele- 
scope level  to  the  range  specified  for  the  stated  heights  of  site : 


Angle  of  rotation  in  minutes  for  height  of  instrument  of— 

Range. 

60  feet. 

81  feet. 

126  feet. 

210  feet. 

282  feet. 

396  feet. 

Telescope  level        

0 

8.576 
9.W2 
10.286 
12.  727 
18.034 
23.552 
34.799 

0 

10.764 
12.216 
13.294 
16.738 
24.501 
31.573 
46.830 

0 

15.451 
17.945 
19.739 
25.332 
39. 582 
48.760 
72.605 
. 

0 

24.202 
28.640 
31.  771 
41.374 
61.000 
80.833 
120.694 

0 
31.702 

37.806 
42.083 
55.122 
81.617 
108.314 
161.  877 

0 

11,000 

43. 576 

9.000 

52. 319 

8000                                     - 

58.409 

6,000 

76.886 

4,000                    

114.249 

3,000 

151.  796 

2,000         

226.984 

LEWIS   DEPRESSION    POSITION   FINDER,    MODEL    OF    1907. 

(See  drawings  Class  22,  Division  21,  drawings  1  to  10,  inclusive,  and  pamphlet  No. 

1876.) 

190.  To  disassemhle  the  internal  mechanism. — Take  off  the  tele- 
scope by  loosening  the  trunnion  center  screws  (4E)  and  pidling 
trunnion  centers  (4T)  out  gradually  to  prevent  the  telescope  from 
jarring.  Remove  the  table  clamp  (4C)  by  driving  out  the  taper 
pin  (4P)  and  unscrewing  the  head  (4Q)  and  taking  out  the  clamp 
screw  (4R)  (left  hand  thread).  Take  off  the  gear  guard  ring  (5D), 
first  removing  the  12  screws  holding  same  to  table.  Remove  the 
5  screws  holding  the  gear  case  (5M)  to  the  table  (5A),  being  careful 
to  note  position  of  long  and  short  screws  and  take  off  the  gear  casie 
(5M).  Unscrew  the  small  headless  screw  in  the  gear  (5H)  and  drive 
out  the  pinion  (5J)  from  the  gear  (5H)  with  a  small  stick  and  hammer. 
Loosen  the  three  table  center  screws  (4L)  and  (4Z)  in  the  body 
about  U  turns  and  lift  off  the  table  (5 A)  (2  men  required),  by  raising 
on  opposite  sides  with  equal  force,  taking  care  not  to  force  parts  or  to 
injure  the  center.  Mark  one  s^ot  of  table  center  (4G)  and  one  table 
center  screw  so  that  the  table  may  be  put  back  in  same  position. 

191.  To  dismantle  the  range  gearing. — Set  the  range  scale  at  1,500 
yards  and  mark  the  position  of  the  range  dial  gear  (3Q),  the  rack  gear 
(3S),  and  the  lower  worm  shaft  gear  (2W).  Remove  the  range  dial 
gear  plate  (3E).  Mark  the  position  of  the  range  pointer  (3TA). 
Remove  the  lower  worm  shaft  gear  (2W),  holding  the  rack  gear  (3S) 
9950—17 5 


G6 

to  prevent  its  rotation.     Remove  the  rack  gear  plate  (3F)  and  the 
rack  gear  (3S).     Assemble  in  the  reversed  order. 

192.  To  disassemble  the  azimuth  gearing. — Remove  the  trunnion 
yoke  screw  (4B)  and  pull  out  the  trunnion  yoke  (4F).  Unscrew  the 
screw  located  directly  under  the  trunnion  yoke  screw  which  holds 
the  table  (5A)  to  the  tabel  center  (4G).  Drive  out  the  table  center 
(4G)  by  tapping  lightly,  on  the  head  of  the  center  screw  (4H).  Do 
not  remove  the  azimuth  circle  (6P)  and  holder  (6Q)  unless  it  is 
necessary.  Never  attempt  to  remove  these  parts  until  after  the 
table  has  been  removed  from  the  body  (6B). 

Remove  the  screw  for  table  (6G)  and  the  small  headless  screw  in  the 
screw  for  azimuth  dial  pinion  (4M)  and  unscrew  the  screw  for  azimuth 
dial  pinion  (4M).  The  azimuth  dial  assembled  (4X)  will  then  drop 
out.  Remove  the  screws  for  azimuth  dial  block  (6E)  [these  are  the 
first  and  fourth  screws  in  the  table  extending  in  a  line  outward  from 
the  azimuth  circle  window  (5B)]  and  slide  out  the  azimuth  dial 
block  (6R)  and  ^oiy  degree  scale  (6S)  assembled.  The  screw  for 
azimuth  dial  pinion  (4M)  and  the  eccentric  for  azimuth  dial  block 
(6D)  may  now  fall  out.  Assemble  in  the  reversed  order.  Make 
sure  that  the  pin  which  is  located  half  in  the  azimuth  dial  pinion  (4D) 
and  half  in  the  azimuth  dial  center  (4N)  is  driven  home.  Otherwise 
backlash  may  be  found  in  the  ^hj  degree  scale  (6S). 

193.  To  remove  the  compensating  mechanism. — Set  the  range  scale 
at  1,500  yards  and  note  the  position  of  the  cam  (2Z)  and  the  pin  for 
bar  (3D).  Take  off  the  worm  shaft  nut  (2P).  Mark  the  position  of 
the  lower  worm  shaft  gear  (2W)  in  reference  to  the  range  dial  gear 
(3Q).  Remove  the  lower  worm  shaft  gear  (2W).  Take  out  the 
four  screws  holding  the  screw  and  gear  case  (2A)  and  lift  it  from  the 
table. 

194.  To  change  the  class  of  an  instrument. — Remove  the  com- 
pensating mechanism  and  the  range  dial  as  described  above.  The 
range  dial  gear  and  the  compensating  mechanism  of  class  required 
may  then  be  assembled  in  the  reversed  order  specified  above.  Take 
care  to  set  all  parts  in  the  same  manner  in  respect  to  each  other  as 
those  removed;  that  is,  the  range  dial  and  the  range  pointer  should  be 
at  1,500  yards,  the  rack  gear  (3S)  at  the  position  marked  and  the 
cam  (2Z)  and  pin  for  bar  (3D)  should  be  in  same  position  as  on  com- 
pensating mechanism  taken  off.  (The  position  of  the  cam  and  pin 
for  bar  is  that  shown  on  Plate  IV  of  pamphlet  No.  1876 — Description 
of  the  Lewis  Depression  Position  Finder,  Model  of  1907.) 

It  is  possible  that  the  hole  through  the  center  of  trunnion  yoke  (4F ) 
will  needs  be  elongated  to  obtain  short-range  readings  at  the  extreme 
readings  on  the  tide  scale.  Test  to  see  that  the  lug  on  the  trunnion 
of  the  telescope  tube  does  not  come  in  contact  with  the  sides  of  this 
clearance  hole. 


67 

195.*  To  disassemble  the  compensating  mechanism. — After  removal 
of  the  compensating  mechanism  which  has  previously  been  set  at 
1,500  yards,  remove  the  two  intermediate  gear  plates  (2BA).  Take 
out  the  two  screws  holding  the  worm  wheel  shaft  bracket  (2B)  to 
the  screw  and  gear  case  (2A).  Unscrew  the  screws  holding  the 
worm  shaft  plate  (2R)  and  draw  out  the  worm  shaft  plate  (2R) 
the  worm  shaft  (2X)  and  the  upper  worm  shaft  gear  (2G)  assembled. 
To  disassemble  the  upper  worm  shaft  gear  (2G)  remove  the  set 
screw  from  it  and  draw  off  the  gear  from  the  worm  shaft.  If  the 
bevel  gear  (2D)  and  the  worm  wheel  (2C)  are  to  be  disassembled, 
first  drive  out  the  taper  pins  (2E)  and  (2YA)  from  the  bevel  gear 
(2D)  and  the  collar  (2ZA).  Remove  the  set  screw  from  the  cam 
and  drive  out  the  taper  pin  (2J)  from  the  cam  (2Z).  Then  drive 
the  cam  shaft  (2L)  into  the  screw  and  gear  case  (2A).  If  the  cam 
is  to  be  removed  loosen  the  screw  holding  the  pin  for  bar  (3D)  and 
push  out  the  pin  for  bar  (3D).  The  cam  may  then  be  slipped  out. 
Note  that  the  tangent  screw  gears  (2HA)  are  marked  for  assembling 
in  a  particular  position  on  the  inner  sleeve  nut  (2EB)  and  the  outer 
sleeve  nut  (2DB).  If  removed,  these  geare  should  be  carefully 
assembled  in  the  same  manner.  The  parts  disassembled  may 
then  be  assembled  without  readjustment  of  the  compensating 
mechanism,  provided  that  the  outer  sleeve  nut  and  the  inner  sleeve 
nut  have  not  been  changed  in  position. 

196.*  If  the  tangent  screw  rail  is  to  be  removed,  measure  and 
record  the  distance  from  the  bottom  of  the  screw  and  gear  case  (2 A) 
to  the  top  of  tangent  screw  rail  (3UA).  After  the  removal  of  screws 
holding  the  tangent  screw  gear  (2HA)  to  the  inner  sleeve  nut  (2EB) 
and  the  outer  sleeve  nut  (2DB),  the  tangent  screw  rail  (3UA)  with 
sleeve  nuts  assembled  may  be  withdrawn  from  the  screw  and  gear 
case  (2A).  The  inner  sleeve  nut  (2EB)  and  the  outer  sleeve  nut 
(2DB)  may  then  be  removed  and  later  the  tangent  screws  (2AA). 
Clean  all  gears  and  all  bearing  surfaces  before  assembling  and  oil  all 
parts.  Examine  small  pieces  for  burrs  and  remove  them  if  found  on 
bearing  surfaces.  Be  exceedingly  careful  in  cleaning  the  threads  of 
tangent  screw  and  sleeve  nut  Oil  these  threads  with  clock  oil.  In 
instruments  of  classes  A  and  AA  the  screws  have  210  threads  per 
inch,  and  any  dirt  or  grit  in  the  threads  will  interfere  with  the  smooth- 
ness of  operation  and  the  accuracy  of  these  parts. 

197.*  Assembly  of  compensating  mechanism. — Reassemble  in  the 
reverse  order,  noting  that  the  lower  numbers  on  the  tide  scale  on 
the  tangent  screw  rail  (3UA)  should  be  over  the  outside  end  af  the 
screw  and  gear  case.  Adjust  the  inner  and  outer  sleeve  nuts  on  the 
tangent  screws  until  the  tangent  screw  rail  is  exactly  parallel  with  the 

*  See  paragraph  11. 


.68 

bottom  surface  of  the  screw  and  gear  case.  Locate  the  cam  (2Z)  so 
that  the  pin  for  bar  (3D)  is  in  the  left  end  of  cam  groove  (see  note 
on  drawing  22-21-8).  Locate  the  intermediate  gear  plates  (2BA)  so 
that  the  intermediate  gears  (2U)  mesh  the  pinion  and  tangent 
screw  gears  (2HA)  without  backlash  and  so  that  the  outer  sleeve  nut 
(2DB)  operates  smoothly  and  without  backlash.  The  assembled 
height  from  the  surface  of  the  tangent  screw  rail  to  the  axis  of  the 
telescope  (axis  of  trunnion  centers)  is  specified  on  drawing  22-21-8. 
If  the  height  of  rail  from  base  of  screw  and  gear  case  is  made  the 
same  as  measured  before  disassembling,  the  rail  should  be  located 
correctly  from  the  axis  of  the  telescope.  It  may  be  noted  that  the 
surface  of  the  table  to  which  the  compensating  mechanism  is  fitted 
is  accurately  scraped  in  reference  to  the  lower  surface  of  the  inner 
hub  of  the  table. 

198.  To  test  correctness  of  assembly} — ^After  assembling  the  table 
test  by  operating  the  outer  sleeve  nut  to  see  that  the  range  scale  may 
be  operated  throughout  the  limits  of  range.  In  case  the  range 
pointer  is  not  correctly  set,  keep  the  range  scale  at  1,500  yards, 
remove  the  table,  take  off  the  lower  worm  shaft  gear  (2W)  and 
move  the  rack  gear  and  pinion  (3U)  to  the  desired  position,  and 
reassemble.  If  the  range  dial  gear  (3Q)  is  limited  in  movement,  lift 
and  block  up  the  table,  and,  if  the  desired  additional  movement  is 
small,  spring  the  range  dial  gear  (3Q)  sufficiently  to  throw  it  out  of 
mesh  with  the  lower  worm  shaft  gear  (2W)  and  move  it  in  the  desired 
direction.  If  the  required  additional  movement  is  considerable,  dis- 
assemble and  reassemble  all  parts,  setting  the  range  dial  gear  (3Q) 
and  the  range  pointer  (3TA)  at  1,500  yards  and  the  cam  (2Z)  so  that 
the  pin  for  bar  (3D)  is  in  the  left  end  of  slot. 

199.  Accuracy  tests. — The  accuracy  of  readings  may  be  measured 
by  comparison  with  a  bar  scale  graduated  in  inches  and  fractional 
parts.  Set  the  height  for  the  given  height  of  site  and  the  range 
scale  at  a  range  of  about  8,000  yards  for  instruments  whose  range 
scales  are  graduated  to  12,000  yards  and  of  about  4,500  yards  for 
other  instruments.  Set  up  the  bar  scale  vertically  at  exactly  100 
feet  distance  from  the  telescope  (trunnion  center)  axis,  so  that  the 
bar  scale  reading  given  in  table  below  for  the  range  setting  specified 
is  intersected  by  the  horizontal  cross  wire.  This  is  calculated  so 
that  the  0  of  scale  corresponds  to  the  ''telescope  level"  position  of 
the  telescope.  Then  by  moving  the  range  mechanism,  without  dis- 
turbing the  compensating  screw,  bring  the  telescope  successively  to 
the  bar  scale  readings  and  read  the  range  registered  on  the  range 
scale.  To  obtain  the  range  error,  subtract  the  measured  range  from 
the  calculated  range. 

1  Collimate  the  telescope  as  described  in  paragraphs  80-85. 


C9 


200.  Data  for  accuracy  tests. 


Range. 

Bar  scale  reading  in  inches  for  a  height  of  instrument  of — 

24  feet. 

60  feet. 

81  feet. 

126  feet. 

210  feet. 

282  feet. 

396  feet. 

8° 

0 

1.684 

1.731 

1.790 

2.043 

2.695 

3.421 

4.948 

0 

2.994. 
3.331 
3.590 
4.443 
6.295 
8.221 
12.148 

0 

3.757 
4.264 
4.640 
5.843 
8.395 
11. 021 
16.348 

0 

5.394 
6.264 
6.890 
8.843 
13.817 
17. 021 
25.348 

0 

8.448 
9.997 
11.090 
14.443 
21.295 
28.221 
42.148 

0 

11.066 
13. 198 
14.690 
19.243 
28.495 
37.  822 
56.548 

0 

11,000 

15. 212 

9,000 

18.264 

8,000 

20  390 

6,000 

26.843 

4,000 

39.  895 

3,000 

53  021 

2,000..  . 

79  348 

If  desired,  the  target  may  be  set  up  at  a  shorter  distance,  provided 
that  the  bar  scale  readings  are  proportionally  reduced. 


SCALE  ARMS  (Group  c). 

201.  Scale  arms  and  all  graduated  surfaces  give  incorrect  results 
if  their  fiducial  edges  for  any  reason  lose  the  form  they  properly 
should  have.  Thus,  the  long  plotting  arms  for  a  Whistler-Hearn 
plotting  board,  if  handled  roughly,  or  if  bent  too  much,  become 
warped  in  one  direction  or  another,  giving  readings  too  great  or  too 
small,  depending  on  the  direction  of  warping.  Such  arms  must  be 
removed  from  the  board,  and  by  careful  reverse,  bending,  peening, 
and  testing  with  a  straightedge,  returned  to  their  original  condition. 
In  tapping  such  arms,  tap  very  lightly  and  carefully,  for  otherwise 
the  tapping  will  result  in  broadening  out  the  distance  between  grad- 
uations, and  thus  in  destroying  the  accm-acy  of  the  arm.  Where 
circular  scales  are  bent  out  of  shape  and  become  eccentric,  a  gage 
must  be  made  for  testing  the  edge  after  correction.  Spoiled  scales 
may  ordinarily  be  replaced  by  new  ones  obtainable  from  the  Frank- 
ford  Arsenal.  If  time,  cost  of  transportation,  or  other  reason  pre- 
vents, new  pieces  must  be  prepared  according  to  the  drawings,  and 
graduated  carefully.  The  index  head  of  a  milling  machine  may  be 
used  if  no  circular  graduating  machine  for  circular  scales  is  avail- 
able. For  straight  scales,  if  no  rectilinear  graduating  machine, 
least  reading  0.001  inch,  is  available,  use  the  best  vernier  gage 
obtainable  for  the  purpose.  Lettering,  numbering,  and  index  marks 
wiU  in  such  cases  ordinarily  have  to  be  stamped  in.  The  stamping 
increases  the  length  of  the  scales;  hence  the  stamping  must  be  done 
before  the  final  graduation,  the  position  of  the  various  numbers 
being  determined  as  closely  as  possible.  If  an  engraving  machine 
is  available,  the  graduating  should  be  done  first  and  the  engraving 
second. 


7.0 

WOODEN  PARTS   (Group  d). 

202.  Wooden  parts  of  instruments,  if  destroyed  or  damaged  so  as 
to  interfere  with  the  action  of  the  other  parts  of  the  same  instru- 
ment, should  be  replaced  when  possible  by  the  same  material  as 
that  originally  used.  The  various  drawings  specify  the  material 
and  its  method  of  preparation,  including  the  linseed  oil  and  varnish 
treatment.  Warping  can  only  be  provided  for  by  increasing  clear- 
ances already  uUowed.  Slotted  instead  of  round  screw  holes,  etc., 
are  suggested  as  means  of  overcoming  difficulties  ii;i  the  adjustment 
of  metal  parts  to  a  wooden  base  which  expands  or  shrinks  unduly 
with  change  of  moisture  in  the  air.  No  absolute  method  can  be 
given  for  such  cases,  and  readjustment  of  all  metal  parts  frequently 
will  be  found  necessary. 

SPECIAL  PARTS   (Group  e). 

203.  The  canvas  charts,  with  the  blue-print  chart  attached,  for 
Pratt  range  board  should  be  kept  habitually  flat  when  not  stretched 
in  the  board.  If-  it  is  desired  to  prepare  new  charts,  obtain  the 
canvas  of  the  size  necessary  and  sew  over  a  stretching  form  corre- 
sponding to  the  frame  of  the  board.  While  stretched  tight  paste 
on  the  blue  print  in  its  proper  position,  giving  careful  attention  to 
the  eyehole.  Sew  edges  of  blue  print  down  after  pasting,  as  they 
will  otherwise  curl  up  and  tear  off. 

204.  The  rubber  covering  of  the  mobile  artillery  board  may  be 
rubbed  up  and  in  a  measure  improved  as  to  elasticity  by  the  use  of 
powdered  sulphur.    Keep  the  rubber  out  of  the  sun  when  practicable. 

205.  The  steel  tapes  issued  with  Weldon  range  finders  should  be 
kept  clean  and  well  oiled  when  not  in  use.  When  using,  avoid  get- 
ting kinks  in  the  steel  ribbon.  Never  drag  the  tape  over  rough  or 
broken  ground.  Before  winding  up,  clean  the  steel  ribbon  as  it 
comes  in  of  all  grit  and  dirt,  for,  if  not,  after  once  entering  the  case, 
the  parts  will  be  rapidly  clogged,  scratched,  and  otherwise  injured. 
Should  a  tape  break,  repair  the  break  by  an  extra  piece  soldered  on, 
or  attached  by  suitable  rivets,  and  of  such  length  as  to  keep  the 
readings  of  the  tape  on  either  side  of  the  break  correct. 

206.  Time-interval  recorders  may  be  repaired  and  adjusted  by 
any  competent  watch  repairer. 

ADDITIONAL.  TESTS. 

207.  For  testing  of  plotting  boards,  if  data  for  observation  points 
is  not  at  hand,  hypothetical  points  should  be  located  in  the  field  of 
fire  at  long  ranges,  and  the  azimuth  and  distances  of  these  points  from 
the  primary  and  secondary  stations  and  from  the  directing  point  of 
the  battery  should  be  calculated.  To  test  a  plotting  board,  set  the 
primary  and  secondary  arms  at  the  calculated  azimuths,  note  errors 


71 


in  the  ranges  from  these  stations  and  errors  in  gun  arm  range  and 
azimuth  from  the  calculated  values. 

208.  In  case  it  is  desired  to  report  the  condition  of  a  plotting  board 
to  an  armament  officer  or  to  Frankford  Arsenal,  it  will  b(b  of  great 
assistance  if  a  complete  test  of  the  board  be  made  and  reported  in 
accordance  with  the  following  form,  in  each  case  reporting  the  model 

and  serial  number:  Tested  for  right  (or  left)  base  line yards 

long  with  ranges  from  . yards  to yards  from  the  gun 

center.  The  errors  of readings  were :  Primary  arms,  maxi- 
mum,    yards;  mean,  yards.  Secondary  arm,  maxi- 
mum,        yards;  mean,    yards.     Gun  arm,  maximum, 

yards;  mean, yards.  Gun  arm  azimuth  circle,  maxi- 
mum,        °;   mean,    °.     The  maximum   error  in  gun 

azimuth  if  the  gun  arm  is  moved  from  1,500  through  inter- 
mediate positions  to  2,500  is °.     The  gun  arm  set  at  the 

azimuth  of  the  normal  is  parallel  to  the  primary  arm  set  at  the  same 

azimuth;  error, °.     The  error  in  azimuth  of  the  gun  arm 

due  to  moving  the  longitudinal  slide  through  the  full  extent  of  its 

movements  is   ° ;  the  error  due  to  moving  the  lateral  slide 

similarly  is   °.     The  primary  (or  secondary)  arm  set  at  the 

azimuth  of  the  base  line  is  parallel  to  the  base  line  arm  with  an  error 

of °.     The  backlash  of  the  gun  azimuth  mechanism  is ° ; 

that  of  the  azimuth  correction  mechanism  is ° ;  that  of  the 

primary  index  box  is ° ;  that  of  the  secondary  index  box  is 

°.     The   base  line   arm  vernier  is  located   correctly;   error, 

°.     With  the  gun  arm  center  over  the  primary  arm  center  the 

maximum  error  of  the  gun  arm  azimuth  circle  compared  with  the 

main  azimuth  circle  is   °.     The  fiducial  edges  of  the  arms 

(naming  them)  vary  from  a  straight  edge  by inches. 

209.  The  following  problems  and  results  are  furnished  for  testing 
other  instruments  of  the  fire-control  systems.  The  instrument  should 
be  set  at  the  given  data  of  the  problem  and  the  results  obtained  on 
the  instrument  compared  with  the  calculated  results. 

Deflection  hoard,  model  of  1905,  for  guns. 
[For  capped  projectiles,  short  points.] 


Service. 

Subcaliber. 

Given: 

Interval — seconds                    .  .  . 

15 

10 

16 

10,000 

30 

90 

11 

6,000 

15 

35 

16 

2,000 

30 

Wind  scale 

65 

Platen  scale      

11 

jiaxige — yards 

2,000 

Gun. 

8  in. 

10  in. 

12  in. 

Sin. 

10  in. 

12  in. 

Sub- 
caliber. 

Sub- 
caliber. 

Result: 

Deflection  scale 

Azimuth  correction  scale 

3.219 
16. 219 

3.323 
16. 323 

3.416 
16.416 

1. 834 
9. 834 

1.854 
9.  854 

1.847 
9.847 

2.643 
15.  64.J 

2.635 
10.635 

72 


Deflection  board,  model  of  1906,  for  12-inch  mortars. 


Given. 

Result. 

Azimuth 

Elevation. 

Deflection. 

Model  of  1890  M. 

Model  of  1886. 

Subcaliber. 

824  lbs. 

1,046  1J>S. 

824  lbs. 

1,046  lbs. 

10» 
145» 
271° 

45° 
55° 

3 
5.50 
0.50 

6.66 
139.44 
263.47 

7.37 
141. 15 
264.54 

7.33 
141.06 
264.47 

7.90 
142.42 
265.34 

8.88 
144.75 
266.79 

Wind  component  indicator. 
[Problem:  Azimuth  of  wind,  135;  azimuth  of  target  arm,  190;  velocity  of  wind,  50.] 


Result: 
Rai  _ 
Deflection  component 9. 0425 


fek  RMge  component 21. 321 


Field-artillery  plotter,  model  of  1907. 


Observation  of  point  settings. 

Relocating  readings. 

Aiming  point  arm. 

Target  arm. 

Gun  arm. 

Aiming  point  arm. 

Target  arm. 

MUs. 

Yards. 

Mils. 

Yards. 

Yards. 

MUs. 

Yards. 

Mils. 

Yards. 

56 
56 

2,000  ;               48 
4,000                 48 

2,000 
4,000 

.       2,828 
5,656 

40 
40 

2,000 
4,000 

16 
16 

2,000 
4,000 

Battery  commander's  ruler,  for  2.95-inch  mountain  gun. 


12.5-pound 
projectUe. 

18-pound 
projectile. 

First 
problem- 

Second 
probleuL 

Third 
problem. 

Fourth 
problem. 

Given: 

Angle  of  site  of  target 

100 

600 

3,800 

363.4 

-20 
1,000 
3,400 

177.3 

100 

600 

3,800 

493.8 

-20 

Range  of  obstacle 

1,000 

Range  of  target 

3,400 

Result: 

Height  of  trajectorv,  calculated 

272.7 

For  3-inch  field  gun. 


First 
problem. 

Second 
problem. 

Third 
problem. 

Fourth 
problem. 

Given: 

Angle  of  site  of  target 

+130 
1,000 
4,600 

282 

-15 

200 

2,800 

64 

+20 
2,400 
5,200 

164 

+50 

Range  of  obstacle 

4,000 

Range  of  target  ...                                 

5,600 

Result: 

Height  of  trajectorv.  calculated 

150 

73 

For  4.7-inch  gun. 


First 
problem. 

Second 
problem. 

Third 
problem. 

Fourth 
problem. 

Given: 

+1.% 
1.000 
6.O00 

2S:!.2 

-15 
200 

2,800 

•12.2 

+  20 
3,800 
6,700 

137. 9 

+50 

Range  of  obstacle 

Range  of  target          .                          i 

6.000 

7  800 

Result: 

Height  of  trajectory,  calculated 

156.1 

Sextant  telemeter,  Type  A,  model  of  1911,  slide  ruler  for  solution  of  triangles. 


First 
problem. 

Second 
problem. 

Third 
problem. 

Given: 

Angle  in  mils                                              

1.600 
7 
65 

9,458 

SOO 
24 

500 

Difference  in  mils 

3  9 

Base 

100  !           36 

Rcsnlt: 

3,001  1      5,402 

INDEX 


All  numbers  refer  to  paragraphs. 

A. 

Aiming  circle,  model  of  1916: 

Angle  of  sight  mechanism,  to  disassemble 153 

Azimuth  worm  mechanism,  to  disassemble 154 

Compass  mechanism,  to  disassemble 155 

Compass  needle,  to  remove 156 

Elbow  prism,  to  clean 149 

Elevation  mechanism,  to  disassemble 151 

Erecting  prism,  to  clean 149 

Eyepiece,  to  disassemble 148 

General  information 147 

Objective,  to  clean 150 

Objective,  to  remove 152 

Objective  prism,  to  clean ! 150 

Azimuth  instrument,  model  of  1900 , • 177 

Adjustment  of  worm .'J . .':  .■'.■ 166 

Azimuth  instrument,  model  of  1910 ,  177 

Adjustment  of  worm , ..t^  ,  166 

Assembly  of 178 

Disassembly  of 177, 178 

B. 

Balsam,  application  of 41 

Deterioi-ation  of 28 

Battery  commander 's  ruler,  test  of 209 

Battery  commander's  telescope,  models  of  1904  and  1905: 

Adjustment  of  telescope 94,  98 

Assembly  of  base 174 

Assembly  of  telescope 87,  90,  91,  93 

Cleaning  of  telescope 86,  87,  89,  91 

Collimation  of 95,  96 

Disassembly  of  base 174-176 

Disassembly  of  telescope 87-93 

Battery  commander's  telescope,  model  of  1915: 

Elevation  worm  mechanism,  to  disassemble 103 

Eye  lens,  to  remove 101 

Eyepiece,  to  disassemble 102 

Objective,  to  remove ^ 100 

Objective  pi-ism,  to  clean 99 

C. 

Cement,  litharge 39, 161 

Cementing  of  optical  surfaces 41 

Chart,  canvas 203 

(75) 


.76 

Cheat,  use  of 6 

Cleaning,  instructions  for 6,  29 

Clinometer,  adjustment  of.* 19 

Use  of 18 

Collimating  telescope.     See  Telescope,  collimating. 

D. 

Deflection  board  for  guns,  test  of 209 

Deflection  board  for  mortars,  test  of 209 

Depression  position  finder,  Lewis,  model  of  1907: 

Adjustment  of  cross  wire 35,  80 

Assembly  of  compensating  mechanism 197 

Assembly  of  range  mechanism 196, 198 

Change  of  class  of 194 

Collimation  of  telescope 81-85 

Disassembly  of  azimuth  mechanism 190, 192 

Disassembly  of  compensating  mechanism 193, 195 

Disassembly  of  range  mechanism. 190, 191 

Test  of \ 199,  200 

Depression  of  position  finder,  Lewis,  type  A,  adjustment  of  prism 66 

Depression  of  position  finder,  Swasey,  tyY>e  A: 

Adjustment  of  telescope 65 

Disassembly  of  base 179 

Disassembly  of  telescope 63,  64 

Depression  position  finder,  Swasey,  types  Al  and  All: 

Adjustment  of  azimuth  worm 166 

Adjustment  of  height  scale 188 

Adjustment  of  range  mechanism 187 

Adjustment  of  telescope 78,  79 

Adjustment  of  telescope  level 77 

Assembly  of  azimuth  mechanism. 179, 185 

,      Assembly  of  range  mechanism 186 

Assembly  of  telescope 76 

Collimation  of  telescope 78 

Disassembly  of  azimuth  mechanism .! 179 

Disassembly  of  curvature  mechanism 183 

Disassembly  of  range  mechanism 180-182, 184 

Disassembly  of  telescope 75,  76 

Test  of 189 

Disassembly,  by  whom 11, 12 

E. 

Erecting  systems,  construction  of 22,  23 

Eyepiece,  adjustment  of 26 

Construction  of , 25 

F. 

Field  artillery  range  finder,  general  information 146 

G. 

Glass,  decomposition  of 27 


77 

H. 

Humidity,  effects  of 7,  27 

L. 

Lens,  adjustment  of 26 

Cementing  of 42 

Cleaning  of 30 

Deterioration  of 27,  28 

Test  of - 33 

Level,  adjustment  of 53,  54, 170-172 

Replacement  of 169 

Test  of 168 

M. 

Mirror,  silvering  of 40 

O. 

Objective,  construction  of 20 

Adjustment  of 26 

Test  of 33 

Observation  telescope,  field,  disassembly  of  telescope 104, 105 

Oiling 6 

Optical  repair  kit 15 

Tool  No.  29 46 

Tool  No.  32 123 

Tool  No.  34 123 

Tool  No.  36 177 

Tool  No.  37 ; 175 

Tool  No.  41 : 174 

Tool  No.  43 185 

Tool  No.  73 81 

Tool  No.  85 16,  48,  51,  81, 127, 128 

,     Tool  No.  86 16,  48,  81, 128 

Tool  No.  87 50,  51 

Tool  No.  88 127 

Tool  No.  89 127 

Tool  No.  90 16, 128 

Tool  No.  98 17, 48,  59,  62,  73,  81 

Tool  No.  99 73 

Tool  No.  101 59 

Tool  No.  102 48 

Tool  No.  103 62 

Tool  No.  104. ■ 157 

9 
P. 

Panoramic  sight,  model  of  1904 : 

Adjustment  of  azimuth  circle 128, 129 

Adjustment  of  prisms. 127, 130-132 

Adjustment  of  reticule 126, 127 

Assembly  of 122 

Cleaning  of - 111,120,121,124 

Disassembly  of Ill,  119, 123, 125 

Sealing  of Ill 


78 

Panoramic  sight,  model  of  1915 : 

Azimuth  mechanism,  to  disassemble 136 

Deflection  mechanism,  to  disassemble 137 

Eye  piece,  to  disassemble 134 

General  information 133 

Objective  lens,  to  remove 138 

Rotating  head  mechanism,  to  disassemble 135 

Plotting  boards  for  mobile  artillery 204 

Test  of • .• . . .  209 

Plotting  boards  for  seacoast  artillery,  backlash  in 165 

Form  for  report  on 208 

,      Test  of ; 207 

Plaster,  use  of 37 

Prism,  adjustment  of 68 

By  whom  disassembled 12 

Cementing  of 43 

Cleaning  of : 31,  32 

Construction  of 18, 19,  23,  24 

Deterioration  of 22,  23,  27,  28 

Plastering  of 37 

Silvering  of 40 

Test  of ^     33 

Q. 

Quadrant.     (5ge  Range  quadrant.). 

R. 

Range  board,  Pratt,  chart  of 203 

Test  of 209 

Range  finder,  Weldon: 

Assembly  of 141-143 

Cleaning  of < 140 

Construction  of. : 139 

Prism  for , 144, 145 

Steel  tape  for 205 

Range  quadrant,  adjustment  of  level 171, 172 

Repairs,  by  whom  made 8,  9, 11, 12 

How  made 5,  8, 164 

Report,  to  whom  made 8 

Reticule,  illumination  of 44 

Mounting  of 34 

{See  also  various  telescopes.) 

Rubber 204 

Ruler,  battery  commander's.     (See  Battery  commander's  ruler.) 

,8. 

Scale  arms 201 

Screw  threads • 13 

Sextant  telemeter,  type  A: 

Adjustment  of..'.. .. .* 160, 162. 163 

Assembly  of 157, 161 

Disassemblv  of 157-159 

Test  of...- ^ 209 

Silvering: 

Mirrors 40 

On  metal 38 


79 

T. 

Tape,  steel 205 

Telescope,  collimating 16, 17 

Telescopic  sight,  models  of  1896  Mi,  1897,  1898,  and  1898  M: 

Adjustment  of 50-58 

Collimation  of 56,  57 

Telescopic  sight,  model  of  1899: 

Assembly  of 47 

Collimation  of 48 

Disassembly  of 46 

Telescopic  sight,  model  of  1902,  collimation  of 59 

Telescopic  sight,  3-inch,  model  of  1904,  Nos.  1-26  inclusive: 

Adjustment  of : 62 

Assembly  of 62 

Disassembly  of 60,  61 

Telescopic  sight,  3-inch,  model  of  1904,  after  No.  26: 

Adjustment  of 73,  74 

Assembly  of 7,  72 

Disassembly  of 69-72 

Telescopic  musket  sight,  model  of  1908: 

Adjustment  of 109 

Disassembling  of 106-108 

Telescopic  musket  sight,  model  of  1913: 

General  information 110 

Time-interval  recorder 206 

Tools.     (See  Optical  repair  kit.) 

W. 

Warping 202 

Wind  component  indicator,  test  of 209 

Wire,  cross.     (See  Reticule.) 

Wooden  part 202 

War  Department, 

Office  of  the  Chief  op  Ordnance, 

Washington,  January  4,  1916. 

December  18, 1906. 

Revised  November  1, 1909. 

Revised  October  9, 1912. 

Revised  January  4, 1916. 

Form  No.  1795. 

Ed.  Aug.  24-17—3000. 

38025-2734-1. 


^ 

^ 

•^ 

<>» 

^ 

\ 

^ 

^ 

^ 

1 

•n 

% 

^ 

1 

k 

*5^ 

t^ 

1 

«0 

?^ 

^ 

^ 

{^ 

V^ 

•^ 

•^J 

^* 


5S 


si! 


y 


-® 


M-r  c.-; 


B 


i^ 


r^n- 


i.-^-'l  i   i 


j^)'*'.   J»»»i»        ''^*>*>a'»5»^» 


I 


I 


A 
/     \ 


Ilii 


^||^^ 


.^  ^  N;  NJ  M  .  g  ^ 

i«^  "  *  If  il|l 


^ 

"°^ 

1*1 

t> 

su 

^ 

l>l 

<J 

•  ^-  i 

^ 

.    ^      ' 

k 

^ 

ne 

K 

k 

H 

k. 

^ 

n[1- 

^ 

1  .^ 

k 

i 

>< 

4= 

'<i 

to 

M 

PLATF   L. 


/92arn/7N  at9L^ 


/^iaA>57m/6hORnL 


,«»  y 


'^^. 


'i/^Df?f^HnoB 


AIMING   circle: 


AIMING   CIRCLE,    MODEL  OF   1916. 


14  DAY  USE 

RETURN  TO  DESK  FROM  WHICH  BORROWED 

This  book  is  due  on  the  last  date  stamped  below,  or 

on  the  date  to  which  renewed. 

Renewed  books  are  subject  to  immediate  recall. 

L 

,.^o'5BWJ 

! 

REC-D  LD 

AUG  14  19S8 

i 

! 
\ 

General  Library 
LD  21-50771-8, '57                                  University  of  California 
(C8481sl0)476                                                     Berkeley 

^ 


YC  64382 


Syracuse.  NJ 


Vj  . 

V-^    • 

it 

/f/r 

UNIVERSITY  OF  CAUFORNIA  UBRARY 

% 


